Semiconductor device and electronic device

ABSTRACT

A semiconductor device in which a circuit and a battery are efficiently stored is provided. In the semiconductor device, a first transistor, a second transistor, and a secondary battery are provided over one substrate. A channel region of the second transistor includes an oxide semiconductor. The secondary battery includes a solid electrolyte, and can be fabricated by a semiconductor manufacturing process. The substrate may be a semiconductor substrate or a flexible substrate. The secondary battery has a function of being wirelessly charged.

TECHNICAL FIELD

The present invention relates to an object, a method, or n manufacturingmethod. In addition, the present invention relates to a process, amachine, manufacture, or a composition of matter. One embodiment of thepresent invention relates to a semiconductor device, a display device, alight-emitting device, a power storage device, a memory device, adriving method thereof, or a manufacturing method thereof. Inparticular, one embodiment of the present invention relates to asemiconductor device, a display device, or a light-emitting device eachincluding an oxide semiconductor.

In this specification and the like, a semiconductor device generallymeans a device that can function by utilizing semiconductorcharacteristics. A display device, an electro-optical device, asemiconductor circuit, and an electronic device include a semiconductordevice in some cases.

BACKGROUND ART

Electronic devices carried around by the users and electronic devicesworn by the users have been actively developed.

Since electronic devices carried around by the users and electronicdevices worn by the users are powered by batteries, their powerconsumption is reduced as much as possible. Particularly in the casewhere a central processing unit (CPU), which consumes a lot of power forits operation, is included in the electronic device, processing of theCPU greatly affects the power consumption of the electronic device.

A semiconductor device including a high-performance integrated circuit(e.g., a CPU) over a plastic or plastic film substrate, which transmitsand receives electric power or signals wirelessly, is described inPatent Document 1.

A semiconductor device in which a register in a CPU is formed using amemory circuit including an oxide semiconductor transistor to reducepower consumption is described in Patent Document 2.

Furthermore, a technique for fabricating a semiconductor element and anall-solid-state battery that includes a solid electrolyte over asemiconductor substrate, for miniaturizing an electronic device, hasbeen proposed in recent years (Patent Document 3).

REFERENCE Patent Document

[Patent Document 1] Japanese Published Patent Application No. 2006-32927

[Patent Document 2] Japanese Published Patent Application No.2013-251884

[Patent Document 3] Japanese Published Patent Application No.2003-133420

DISCLOSURE OF INVENTION

The details of the power consumption of an electronic device including aCPU will be described. The power consumption can be roughly classifiedinto power consumed by a CPU, power consumed by systems around the CPU,and power consumed by a plurality of input/output devices and peripheraldevices connected to the inside or outside of the electronic device. Thepower consumed by systems around the CPU includes a loss in a converter,a loss in a wiring pattern, and a power consumed by bus, a controller,and the like.

When an electronic device is reduced in size or thickness, a battery isalso subjected to the limitation. As for a battery, however, decrease involume leads to decrease in capacity. Thus, a circuit, a battery, andthe like are stored in a smaller space.

Furthermore, a battery generates heat by charge and discharge, which maythermally affect the surrounding area.

As an electronic device is reduced in size and a circuit, a battery, andthe like are stored in a smaller space, how to control the powerconsumption and heat generation becomes a problem.

One embodiment of the present invention provides a novel semiconductordevice, a semiconductor device in which a circuit and a battery areefficiently stored, a semiconductor with small power consumption, or asemiconductor device with reduced heat generation.

Furthermore, one embodiment of the present invention provides anelectronic device having a novel structure, specifically, an electronicdevice having a novel structure that can be changed in form in variousways. More specifically, a wearable electronic device that is used whilebeing worn on the body and an electronic device that is used while beingimplanted in the body are provided.

Note that the description of a plurality of objects does not mutuallypreclude the existence. Note that one embodiment of the presentinvention does not necessarily achieve all the objects listed above.Objects other than those listed above are apparent from the descriptionof the specification, drawings, and claims, and also such objects couldbe an object of one embodiment of the present invention.

One embodiment of the present invention is a semiconductor deviceincluding a first transistor, a second transistor, and a secondarybattery. The first transistor, the second transistor, and the secondarybattery are provided over a substrate. A channel region of the firsttransistor includes silicon. A channel region of the second transistorincludes an oxide semiconductor. The secondary battery includes a solidelectrolyte.

In the above embodiment, the substrate is preferably flexible.

In the above embodiment, the secondary battery preferably has a functionof being wirelessly charged.

In the above embodiment, the secondary battery preferably includeslithium. In addition, an insulating film including halogen may beprovided between the secondary battery and the first transistor orbetween the secondary battery and the second transistor.

In the above embodiment, a cooling device may be provided over thesecondary battery.

In the above embodiment, the secondary battery is preferably fabricatedby a semiconductor manufacturing process.

One embodiment of the present invention is an electronic deviceincluding a display device and the semiconductor device according to theabove embodiment.

According to one embodiment of the present invention, it becomespossible to provide a novel semiconductor device, a semiconductor devicein which a circuit and a battery are efficiently stored, a semiconductordevice with small power consumption, or a semiconductor device withreduced heat generation.

Furthermore, according to one embodiment of the present invention, itbecomes possible to provide an electronic device with a novel structure.Specifically, it becomes possible to provide an electronic device havinga novel structure that can be changed in form in various ways. Morespecifically, it becomes possible to provide a wearable electronicdevice that is used while being worn on the body and an electronicdevice that is used while being implanted in the body.

Note that the description of these effects does not disturb theexistence of other effects. One embodiment of the present invention doesnot necessarily achieve all the effects listed above. Other effects willbe apparent from and can be derived from the description of thespecifications the drawings, the claims, and the like.

BRIEF DESCRIPTION OF DRAWINGS

In the accompanying drawings:

FIG. 1 is a block diagram illustrating one embodiment of the presentinvention;

FIG. 2 is a cross-sectional view of a semiconductor device of oneembodiment of the present invention;

FIG. 3 is a cross-sectional view of a semiconductor device of oneembodiment of the present invention;

FIG. 4 is a cross-sectional view of a semiconductor device of oneembodiment of the present invention;

FIGS. 5A and 5B are a top view and a cross-sectional view, respectively,illustrating one embodiment of the present invention;

FIGS. 6A and 6B are a top view and a cross-sectional view, respectively,illustrating one embodiment of the present invention;

FIGS. 7A and 7B are a top view and a cross-sectional view, respectively,illustrating one embodiment of the present invention;

FIGS. 8A and 8B are each a cross-sectional view of a battery of oneembodiment of the present invention;

FIG. 9A is a top view and FIGS. 9B to 9D are cross-sectional views of atransistor included in one embodiment of the present invention;

FIGS. 10A and 10B are a cross-sectional view of a transistor and itsenergy band diagram, respectively, included in one embodiment of thepresent invention;

FIG. 11A is a top view and FIGS. 11B to 11D are cross-sectional views ofa transistor included in one embodiment of the present invention;

FIGS. 12A to 12F each illustrate an electronic device according to oneembodiment of the present invention;

FIGS. 13A and 13B each illustrate an electronic device according to oneembodiment of the present invention;

FIG. 14 illustrates an electronic device according to one embodiment ofthe present invention;

FIGS. 15A and 15B each illustrate an electronic device according to oneembodiment of the present invention; and

FIG. 16 is a cross-sectional view of a semiconductor device of oneembodiment of the present invention.

MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments will be described with reference to drawings.However, the embodiments can be implemented with various modes. It willbe readily appreciated by those skilled in the art that modes anddetails can be changed in various ways without departing from the spiritand scope of the present invention. Thus, the present invention shouldnot be interpreted as being limited to the following description of theembodiments. In addition, in the following embodiments and examples, thesame portions or portions having similar functions are denoted by thesame reference numerals in different drawings and description thereofwill not be repealed.

In the drawings, the size, the layer thickness, or the region isexaggerated for clarity in some cases. Therefore, embodiments of thepresent invention are not limited to such a scale. Note that thedrawings are schematic views showing ideal examples, and embodiments ofthe present invention are not limited to shapes or values shown in thedrawings.

Note that in this specification, ordinal numbers such as “first”,“second”, and “third” are used in order to avoid confusion amongcomponents, and the terms do not limit the components numerically.

Note that in this specification, terms for describing arrangement, suchas “over” “above”, “under”, and “below”, are used for convenience indescribing a positional relation between components with reference todrawings. Furthermore, the positional relation between components ischanged as appropriate in accordance with a direction in which eachcomponent is described. Thus, the positional relation can be describedin different ways as appropriate depending on the situation, withoutbeing limited to the term used in this specification.

In this specification and the like, a transistor is an element having atleast three terminals of a gate, a drain, and a source. In addition, thetransistor has a channel region between a drain (a drain terminal, adrain region, or a drain electrode layer) and a source (a sourceterminal, a source region, or a source electrode layer), and current canflow through the drain, the channel region, and the source. Note that inthis specification and the like, a channel region refers to a regionthrough which current mainly flows.

Furthermore, functions of a source and a drain might be switched whentransistors having different polarities are employed or a direction ofcurrent flow is changed in circuit operation, for example. Therefore,the terms “source” and “drain” can be switched in this specification andthe like.

Note that in this specification and the like, the expression“electrically connected” includes the case where components areconnected through an “object having any electric function”. There is noparticular limitation on an “object having any electric function” aslong as electric signals can be transmitted and received betweencomponents that are connected through the object. Examples of an “objecthaving any electric function” are a switching element such as atransistor, a resistor, an inductor, a capacitor, and elements with avariety of functions as well as an electrode and a wiring.

Embodiment 1 Block Diagram of Device

FIG. 1 is a block diagram of a device 10 that is one embodiment of thepresent invention.

The device 10 of this embodiment includes a control module 15, a displaymodule 21, and a communication module 26. The control module 15 is acontroller that controls the entire device 10, communication, anddisplay of information on a display portion 16.

The control module 15 includes a CPU 11, a battery 12, a regulator 13,and a wireless receiving portion 14.

The display module 21 includes the display portion 16, a display drivercircuit 19, a battery 17, a regulator 18, and a wireless receivingportion 20.

The communication module 26 includes a communication circuit 22, abattery 23, a regulator 24, and a wireless receiving portion 25.

A regulator is an electronic circuit that keeps an output voltage orcurrent constant. A regulator is classified into two kinds, a linearregulator and a switching regulator, depending on the amount of electricload or the like. A switching regulator is also called a DC-DCconverter.

Each module includes a regulator and a battery. Each battery is asecondary battery, which can be charged and discharged repeatedly, andis connected to a circuit in order that it can be wirelessly charged.The batteries are electrically connected to the respective wirelessreceiving portions via the respective regulators. Each regulatorsupplies necessary electric power or signals to the functional circuit,from the connected battery. In addition, each regulator also has afunction of preventing overcharge and the like when the connectedbattery is charged.

In the device 10, each of the modules can be turned on or turned offindependently. The operation system that selectively drives only themodule to be used can reduce power consumption of the device 10.

For example, when the user looks at information on the display portion16 without using a communication function, the communication circuit 22is in an off state where the battery 23 is not used in order thatelectric power to the communication circuit 22 is blocked in thecommunication module 26, while the display module 21 and the controlmodule 15 are in an on state.

Furthermore, for a still image, once the still image is displayed on thedisplay portion 16 with the display module 21 and the control module 15being in an on state, the still image can be kept displayed while onlythe display module 21 is in an on state even after the control module 15is turned off with the still image being displayed. In that case, thecontrol module 15 is not operated although the still image is displayed,and the power consumed by the control module 15 can apparently be zero.Note that when transistors of the display portion 16 use an oxidesemiconductor layer with low off-state current (e.g., an oxide materialincluding In, Ga, and Zn), or when the display portion 16 includes amemory for each of the pixels, the still image can be kept displayed fora certain period even when the supply of electric power from the battery17 is blocked after the still image is displayed.

In this manner, a battery is provided for each of the components to beused in the electronic device, and only the component in use isselectively driven, whereby the power consumption can be reduced.

Note that a memory cell including an oxide semiconductor transistor ispreferably used for a register in the CPU 11. With the use of an oxidesemiconductor transistor in the CPU 11, even in the case where theoperation of the CPU 11 is temporarily stopped and the supply of thepower supply voltage is stopped, data can be held and power consumptioncan be reduced. Specifically, for example, while a user of a personalcomputer does not input data to an input device such as a keyboard, theoperation of the CPU 11 can be stopped, whereby the power consumptioncan be reduced.

Furthermore, the use of oxide semiconductor transistors as thetransistors used for the regulators 13, 18, and 24 can reduce powerconsumption because of the small off-state current. In particular, aregulator (DC-DC converter) including a control circuit including oxidesemiconductor transistors can operate at a temperature of 150° C. orhigher. Thus, such a DC-DC converter is preferably used for anelectronic device that is likely to operate at high temperatures.

In this embodiment, an example in which the display module 21, thecontrol module and the communication module 26 each have a battery isdescribed; however, the total number of batteries is not limited tothree. The electronic device may additionally include functional modulesand their batteries, in which case the electronic device has four ormore batteries in total.

For example, if an exterior body of the device 10 is formed of aflexible material, a wearable device that is used while being worn onthe body can be provided. In that case, if small-sized batteries aredispersedly arranged in the device 10, a feeling of weight can bereduced as compared to an electronic device having a single largebattery. In addition, even if the individual small-sized batterygenerates heat, it does not ruin the comfort of wearing the device.

Next, a semiconductor device that can be used for the device 10 will bedescribed with reference to FIGS. 2 to 4.

Structural Example 1 of Semiconductor Device

FIG. 2 shows a cross-sectional view of a semiconductor device 1000including a transistor 720, a transistor 730, and a battery 740 that areformed over the same substrate. The transistor 720 is provided over asubstrate 700, the transistor 730 is provided over the transistor 720,and the battery 740 is provided over the transistor 730.

The semiconductor device 1000 includes the substrate 700, the transistor720, an element isolation layer 727, an insulating film 731, thetransistor 730, an insulating film 732, an insulating film 741, thebattery 740, an insulating film 742, plugs 701, 703, 704, and 706, andwirings 702, 705, and 707. The transistor 720 includes a gate electrode726, a gate insulating film 724, a sidewall insulating layer 725, animpurity region 721 functioning as a source region or a drain region, animpurity region 722 functioning as a lightly doped drain (LDD) region oran extension region, and a channel region 723.

The impurity concentration is higher in the impurity region 721 than inthe impurity region 722. The impurity region 721 and the impurity region722 can be formed in a self-aligned manner with the gate electrode 726and the sidewall insulating layer 725 used as a mask.

As the substrate 700, a single crystal semiconductor substrate or apolycrystalline semiconductor substrate of silicon or silicon carbide, acompound semiconductor substrate of silicon germanium, asilicon-on-insulator (SOI) substrate, or the like may be used. Atransistor manufactured using a semiconductor substrate can operate athigh speed easily. In the where a p-type single crystal siliconsubstrate is used as the substrate 700, an impurity element impartingn-type conductivity may be added to part of the substrate 700 to form ann-well, and a p-type transistor can be formed in a region where then-well is formed. As the impurity element imparting n-type conductivity,phosphorus (P), arsenic (As), or the like can be used. As the impurityelement imparting p-type conductivity, boron (B) or the like may beused.

Alternatively, the substrate 700 may be an insulating substrate overwhich a semiconductor film is provided. Examples of the insulatingsubstrate include a glass substrate, a quartz substrate, a plasticsubstrate, a metal substrate, a stainless steel substrate, a substrateincluding stainless steel foil, a tungsten substrate, a substrateincluding tungsten foil, a flexible substrate, an attachment film, paperincluding a fibrous material, and a base film. As an example of a glasssubstrate, a barium borosilicate glass substrate, an aluminoborosilicateglass substrate, a soda lime glass substrate, or the like can be given.Examples of a flexible substrate include a flexible synthetic resin suchas plastics typified by polyethylene terephthalate (PET), polyethylenenaphthalate (PEN), and polyether sulfone (PES), and acrylic. Examples ofan attachment film are attachment films formed using polypropylene,polyester, polyvinyl fluoride, polyvinyl chloride, and the like.Examples of a base film are base films formed using polyester,polyamide, polyimide, aramid, epoxy, an inorganic vapor deposition film,and paper.

Alternatively, a semiconductor element may be formed using onesubstrate, and then, transferred to another substrate. Examples of asubstrate to which a semiconductor element is transferred include, inaddition to the above-described substrates, a paper substrate, acellophane substrate, aramid film substrate, a polyimide film substrate,a stone substrate, a wood substrate, a cloth substrate (including anatural fiber (e.g., silk, cotton, or hemp), a synthetic fiber (e.g.,nylon, polyurethane, or polyester), a regenerated fiber (e.g., acetate,cupra, rayon, or regenerated polyester, or the like), a leathersubstrate, and a rubber substrate. When such a substrate is used, atransistor with excellent properties or a transistor with low powerconsumption can be formed, a device with high durability, or high heatresistance can be provided, or reduction in weight or thickness can beachieved.

The transistor 720 is separated from other transistors formed on thesubstrate 700 by an element isolation layer 727.

As the transistor 720, a transistor containing silicide (salicide) or atransistor which does not include a sidewall insulating layer may beused. When a structure that contains silicide (salicide) is used,resistance of the source region and the drain region can be furtherlowered and the speed of the semiconductor device can be increased.Furthermore, the semiconductor device can be operated at low voltage;thus, power consumption of the semiconductor device can be reduced.

When a first semiconductor material is used for the transistor 720 and asecond semiconductor material is used for the transistor 730, the firstsemiconductor material and the second semiconductor material arepreferably material having different band gaps. For example, the firstsemiconductor material can be a semiconductor material other than anoxide semiconductor (examples of such a semiconductor material includesilicon (including strained silicon), germanium, silicon germanium,silicon carbide, gallium arsenide, aluminum gallium arsenide, indiumphosphide, gallium nitride, and an organic semiconductor), and thesecond semiconductor material can be an oxide semiconductor. Atransistor using a material other than an oxide semiconductor, such assingle crystal silicon, can operate at high speed easily. In contrast, atransistor including an oxide semiconductor has a low off-state current.

The details of the oxide semiconductor transistor will be describedlater in Embodiment 3.

Here, in the case where a silicon-based semiconductor material is usedfor the transistor 720 provided in a lower portion, hydrogen in aninsulating film provided in the vicinity of the semiconductor film ofthe transistor 720 terminates dangling bonds of silicon; accordingly,the reliability the transistor 720 can be improved. Meanwhile, in thecase where an oxide semiconductor is used for the transistor 730provided in an upper portion, hydrogen in an insulating film provided inthe vicinity of the semiconductor film of the transistor 730 becomes afactor of generating carriers in the oxide semiconductor; thus, thereliability of the transistor 730 might be decreased. Therefore, in thecase where the transistor 730 using an oxide semiconductor is providedover the transistor 720 using a silicon-based semiconductor material, itis particularly effective that the insulating film 731 having a functionof preventing diffusion of hydrogen is provided between the transistors720 and 730. The insulating film 731 makes hydrogen remain in the lowerportion, thereby improving the reliability of the transistor 720. Inaddition, since the insulating film 731 suppresses diffusion of hydrogenfrom the lower portion to the upper portion, the reliability of thetransistor 730 can also be improved.

The insulating film 731 can be, for example, formed using aluminumoxide, aluminum oxynitride, gallium oxide, gallium oxynitride, yttriumoxide, yttrium oxynitride, hafnium oxide, hafnium oxynitride, oryttria-stabilized zirconia (YSZ).

Furthermore, the insulating film 732 having a function of preventingdiffusion of hydrogen is preferably formed over the transistor 730 tocover the transistor 730 including an oxide semiconductor film. For theinsulating film 732, a material that is similar to that of theinsulating film 731 can be used, and in particular, an aluminum oxidefilm is preferably used. An aluminum oxide film has a high shielding(blocking) effect of preventing penetration of both oxygen andimpurities such as hydrogen and moisture. Thus, by using an aluminumoxide film as the insulating film 732 covering the transistor 730,release of oxygen from the oxide semiconductor film included in thetransistor 730 can be prevented and entry of water and hydrogen into theoxide semiconductor film can be prevented.

The plugs 701, 703, 704, and 706 and the wirings 702, 705, and 707preferably have a single-layer structure or a stacked-layer structure ofa conductive film containing a low-resistance material selected fromcopper (Cu), tungsten (W), molybdenum (Mo), gold (Au), aluminum (Al),manganese (Mn), titanium (Ti), tantalum (Ta), nickel (Ni), chromium(Cr), lead (Pb), tin (Sn), iron (Fe), and cobalt (Co), an alloy of sucha low-resistance material, or a compound containing such a material asits main component. It is particularly preferable that the plugs and thewirings be formed using a Cu—Mn alloy, in which case manganese oxideformed at the interface with an insulator containing oxygen has afunction of preventing Cu diffusion.

The battery 740 is a secondary battery, which can be charged anddischarged repeatedly, and an all-solid-state battery including a solidelectrolyte. Furthermore, in order to enable wireless charging, thebattery 740 is electrically connected to a wireless receiving portionvia a regulator.

In addition, the battery 740 can be fabricated with the use of asemiconductor manufacturing process. Note that the semiconductormanufacturing process refers to methods in general that are used formanufacturing semiconductor devices, such as a film formation process, acrystallization process, a plating process, a cleaning process, alithography process, an etching process, a polishing process, animpurity implantation process, or a heat treatment process.

The details of the battery 740 will be described later in Embodiment 2.

The insulating film 741 can be formed to have a single-layer structureor a stacked-layer structure using one or more of silicon oxide, siliconoxynitride, silicon nitride oxide, silicon nitride, aluminum oxide,aluminum nitride, aluminum oxynitride, hafnium oxide, zirconium oxide,yttrium oxide, gallium oxide, lanthanum oxide, cesium oxide, tantalumoxide, and magnesium oxide.

In the case where the battery 740 includes lithium, the insulating film741 preferably has a function of preventing (blocking) diffusion oflithium. When lithium that is included in the battery 740 enters asemiconductor element (the transistor 720 or the transistor 730) as amovable ion, the semiconductor element deteriorates. With the insulatingfilm 741 blocking lithium ions, a highly reliable semiconductor devicecan be provided.

In the case where the battery 740 includes lithium, the insulating film741 preferably includes halogen such as fluorine, chlorine, bromine, oriodine. When the insulating film 741 includes halogen, the halogen iseasily combined with lithium that is an alkali metal. Then, lithium isfixed in the insulating film 741, whereby diffusion of lithium to theoutside of the insulating film 741 can be prevented.

In the case where the insulating film 741 is formed of silicon nitrideby a chemical vapor deposition (CVD) method, for example, when ahalogen-containing gas is mixed in a source gas at 3% to 6% (volumeratio), e.g., at 5%, the obtained silicon nitride film includes thehalogen. The concentration of the halogen element included in theinsulating film 741, measured by secondary ion muss spectrometry (SIMS),is greater than or equal to 1×10¹⁷ atoms/cm³, preferably greater than orequal to 1×10¹⁸ atoms/cm³, and more preferably greater than or equal to1×10¹⁹ atoms/cm³.

The insulating film 742 has a function of protecting the battery 740. Asthe insulating film 742, for example, an insulating material such as aresin (e.g., a polyimide resin, a polyamide resin, an acrylic resin, asiloxane resin, an epoxy resin, or a phenol resin), glass, an amorphouscompound, or ceramics can be used. Furthermore, a layer containingcalcium fluoride or the like may be provided as a water absorption layerbetween resin layers. The insulating film 742 can be formed by a spincoating method, an ink-jet method, or the like. Alternatively, theinsulating film 742 can be formed to have a single-layer structure or alayered structure using one or more of silicon oxide, siliconoxynitride, silicon nitride oxide, silicon nitride, aluminum oxide,aluminum nitride, aluminum oxynitride, hafnium oxide, zirconium oxide,yttrium oxide, lanthanum oxide, gallium oxide, lanthanum oxide, cesiumoxide, tantalum oxide, and magnesium oxide.

The semiconductor device 1000 may further include a semiconductorelement over the battery 740. In that case, the insulating film 742preferably has a function of presenting (blocking) diffusion of lithium,as with the insulating film 741. With the insulating film 742 blockinglithium, a highly reliable semiconductor device can be provided.

In the case where a semiconductor element is formed over the battery740, the insulating film 742 preferably includes halogen such asfluorine, chlorine, bromine, or iodine, as with the insulating film 741.With the insulating fil 742 including halogen, the halogen is easilycombined with lithium that is an alkali metal, whereby diffusion oflithium to the outside of the insulating film 742 can be prevented.

In FIGS. 2 to 4, regions where reference numerals and hatching patternsare not given show regions formed of an insulator. These regions can beformed using an insulator containing at least one of aluminum oxide,aluminum nitride oxide, magnesium oxide, silicon oxide, siliconoxynitride, silicon nitride oxide, silicon nitride, gallium oxide,germanium oxide, yttrium oxide, zirconium oxide, lanthanum oxide,neodymium oxide, hafnium oxide, tantalum oxide, and the like.Alternatively, in these regions, an organic resin such as a polyimideresin, a polyamide resin, an acrylic resin, a siloxane resin, an epoxyresin, or a phenol resin can be used.

The semiconductor device 1000 in FIG. 2 preferably includes a coolingdevice such as a heat sink, a water-cooling cooler, or a cooling fanover the battery 740. The provision of the cooling device can prevent amalfunction of the semiconductor device 1000 caused by heat generationof the battery 740.

The semiconductor device 1000 in FIG. 2 may include an air gap (a spaceof a vacuum layer) between the battery 740 and the transistor 730. Thecross-sectional view of such a case shown in FIG. 16. A semiconductordevice 1300 shown in FIG. 16 includes an air gap 762 between the battery740 and the transistor 730. The air gap 762 can be formed by forming aninsulating film 763 having low coverage over an insulating film 701having a trench. For each of the insulating films 761 and 763, aninsulator including one or more of the following can be used: aluminumoxide, aluminum nitride oxide, silicon oxide, silicon oxynitride,silicon nitride oxide, silicon nitride, and the like. The provision ofthe air gap 762 under the battery 740 can prevent heat generated in thebattery 740 from being conducted to the transistor 730 and thetransistor 720. Thus, malfunctions of the transistor 720 and thetransistor 730 caused by heat can be prevented.

Although the battery 740 is provided over the transistor 720 and thetransistor 730 in FIG. 2, the battery 740 may be provided between thetransistor 720 and the transistor 730. In that case the transistor 720,the battery 740, and the transistor 730 are formed in this order. In thecase where formation of the battery 740 requires heat treatment at sucha high temperature as will destroy the transistor 730 in particular, itis preferable to from the transistor 730 after forming the battery 740.

The circuits of the CPU 11 or the regulators 13, 18, and 24 included inthe device 10 in FIG. 1 are fabricated using the transistor 720 and thetransistor 730, and the battery 740 that supplies power to she circuitsis fabricated over the same substrate as that of the circuits, forexample, whereby the device 10 can be reduced in size or thickness.

Structural Example 2 of Semiconductor Device

Although the transistor 720 in FIG. 2 is a planar transistor, the formof the transistor 720 is not limited thereto. For example, a FIN-typetransistor, a TRI-GATE transistor or the like can be used. An example ofa cross-sectional view in that case is shown in FIG. 3.

A semiconductor device 1100 shown in FIG. 3 is different from thesemiconductor device 1000 in FIG. 2 in that it includes FIN-typetransistors 750 provided over the substrate 700. In FIG. 3, thetransistor 750 on the left side is a cross-sectional view in the channellength direction of the transistor, and the transistor 750 on the rightside is a cross-sectional view in the channel width direction of thetransistor.

In FIG. 3, an insulating film 757 is provided over the substrate 700.The substrate 700 includes a protruding portion with a thin tip (alsoreferred to a fin). Note that an insulating film may be provided overthe protruding portion. The insulating film functions as a mask furpreventing the substrate 700 from being etched when the projectingportion is formed. Alternatively, the protruding portion may not havethe thin tip; a protruding portion with a cuboid-like protruding portionand a protruding portion with a thick tip are permitted, for example. Agate insulating film 754 is provided over the protruding portion of thesubstrate 700, and a gate electrode 750 and a sidewall insulating layerare formed thereover. In the substrate 700, an impurity region 751functioning as a source region or a drain region, an impurity region 752functioning as an LDD region or an extension region, and a channelregion 753 are formed. Note that here is shown an example in which thesubstrate 700 includes the protruding portion; however, a semiconductordevice of one embodiment of the present invention is not limitedthereto. For example, a semiconductor region having a protruding portionmay be formed by processing an SOI substrate.

For the other components of the semiconductor device 1100, thedescription of the semiconductor device 1000 is referred to.

Structure Example 3 of Semiconductor Device

A semiconductor device 1200 shown in FIG. 4 is different from thesemiconductor device 1000 in FIG. 2 in that the battery 740 is below thetransistor 730.

For the semiconductor device 1200 having the structure shown in FIG. 4,plugs and wirings connected to the transistor 720 can be funned at thesame time as plugs and wirings connected to the battery 740, whereby theprocess can be simplified. Furthermore, in the case where formation ofthe battery 740 requires heat treatment at such a high temperature aswill destroy the plug 701 or the wiring 702, the plug 701 and the wiring702 need to be formed after the battery 740 is formed. In that case, itis preferable to provide the transistor 720 and the battery 740 at thesame level as shown in FIG. 4.

In FIG. 4, the battery 740 is formed after the transistor 720 is formed;however, the transistor 720 may be formed after the battery 740 isformed first. In the case where formation of the battery 740 requiresheat treatment at such a high temperature as will destroy the transistor720 in particular, it is preferable to form the battery 740 first andthen form the transistor 720.

For the other components of the semiconductor device 1200, thedescription of the semiconductor device 1000 is referred to.

The structures and methods described in this embodiment can beimplemented by being combined as appropriate with any of the otherstructures and methods described in the other embodiments.

Embodiment 2

In this embodiment, the details and structural examples of the batterymentioned in Embodiment 1 will be described with reference to drawings.

Structural Example 1 of Battery

FIG. 5A is a top view of a battery 100, and FIG. 5B shows across-sectional view taken along a dashed-dotted line X-Y in FIG. 5A. InFIG. 5A, some components are enlarged, reduced in size, or omitted foreasy understanding.

The battery 100 shown in FIG. 5A includes an insulating film 101, apositive electrode current collector layer 102 over the insulating film101, a positive electrode active material layer 103 over the positiveelectrode current collector layer 102, a solid electrolyte layer 104over the positive electrode active material layer 103, a negativeelectrode active material layer 105 over the solid electrolyte layer104, and a negative electrode current collector layer 106 over thenegative electrode active material layer 105. The positive electrodecurrent collector layer 102 and the positive electrode active materiallayer 103 function as a positive electrode, and the negative electrodecurrent collector layer 106 and the negative electrode active materiallayer 105 function as a negative electrode. In addition, an insulatingfilm 107 is formed over the negative electrode current collector layer100, and a wiring 108 is formed in an opening portion of the insulatingfilm 107. The wiring 108 is electrically connected to the positiveelectrode current collector layer 102 or the negative electrode currentcollector layer 106.

Although not shown in the drawing, a lithium layer may be formed at theinterface between the solid electrolyte layer 104 and the positiveelectrode active material layer 103 or at the interface between thesolid electrolyte layer 104 and the negative electrode active materiallayer 105. The lithium layer is for supplying (or predoping) lithiumserving as a carrier to the positive electrode active material layer orthe negative electrode active material layer in the battery 100. Thelithium layer may be formed over the entire surface of a layer overwhich the lithium layer is to be formed. Furthermore, a copper layer ora nickel layer may be formed in contact with the lithium layer. Thecopper layer or the nickel layer has a shape substantially the same asthat of the lithium layer. The copper layer or the nickel layer canfunction as a current collector when the positive electrode activematerial layer or the negative electrode active material layer ispredoped with lithium from the lithium layer.

Note that the predoping may be performed so that all the lithiumincluded in the lithium layer is doped to the positive electrode activematerial layer or the negative electrode active material layer or sothat part of the lithium layer is left after the predoping. The part ofthe lithium layer left after the predoping can be used to compensatelithium lost by irreversible capacity due to charge and discharge of thebattery.

For the details of the insulating film 101, the description regardingthe insulating film 741 in Embodiment 1 may be referred to.

The positive electrode current collector layer 102, the positiveelectrode active material layer 103, the negative electrode activematerial layer 105, and the negative electrode current collector layer106 can be formed by a sputtering method, a CVD method, nanoimprintlithography, an evaporation method, or the like. When a sputteringmethod is used, it is preferable to use a DC power supply rather than anRF power supply for deposition. A sputtering method using a DC powersupply is preferable because the deposition rate is high and thus cycletime is short. The thickness of each of the positive electrode currentcollector layer 102, the positive electrode active material layer 103,the negative electrode active material layer 105, and the negativeelectrode current collector layer 106 may be greater than or equal to100 nm and less than or equal to 100 μm, for example.

The positive electrode current collector layer 102 may be formed to havea single-layer or layered structure using one or more of titanium (Ti),aluminum (Al), gold (Au), and platinum (Pt). Alternatively, asingle-layer or layered conductive film including an alloy of the abovemetals or a compound containing any of these as a main component may beused.

The positive electrode active material layer 103 may be formed to have asingle-layer or layered structure using one or more of lithiumcobaltate, lithium iron phosphate, lithium manganite, lithium nickelate,and vanadium oxide.

Furthermore, the positive electrode active material layer 103 may beformed using an olivine-type lithium-containing complex phosphate.Typical examples of a lithium-containing complex phosphate(LimPO₄(general formula) (M is one or more of Fe(II), Mn(II), Co(II),and Ni(II))) are LiFePO₄, LiNiPO₄, LiCoPO₄, LiMnPO₄, LiFe_(a)Ni_(b)PO₄,LiFe_(a)Co_(b)PO₄, LiFe_(a)Mn_(b)PO₄, LiNi_(a)Mn_(b)PO₄ (a+b≤1, 0<a<1,and 0<b<1), LiFe_(c)Ni_(d)Co_(e)PO₄, LiFe_(c)Ni_(d)Mn_(e)PO₄,LiNi_(c)Co_(d)Mn_(e)PO₄ (c+d+e≤1, 0<c<1, 0<d<1, and 0<e<1), andLiFe_(f)Ni_(g)Co_(h)Mn_(i)PO₄ (f+g+h+i≤1, 0<f<1, 0<g<1, 0<h<1, and0<i<1).

An inorganic solid electrolyte that can be formed by a sputteringmethod, an evaporation method, or a CVD method is used for the solidelectrolyte layer 104. Examples of the inorganic solid electrolyte are asulfide-based solid electrolyte and an oxide-based solid electrolyte.

Examples of the sulfide-based solid electrolyte are lithium complexsulfide materials such as Li₇P₃S₁₁, Li_(3.25)P_(0.95)S₄, Li₁₀GeP₂S₁₂,Li_(3.25)Ge_(0.25)P_(0.75)S₄, Li₂S—P₂S₅, Li₂S—GeS₂, Li₂S—SiS₂—Li₃PO₄,Li₂S—SiS₂—Ga₂S₃, Li₂S—SiS₂—Li₄SiO₄, LiI—Li₂S—P₂S₅, LiI—Li₂S—B₂S₃, andLiI—Li₂S—SiS₂.

Examples of the oxide-based solid electrolyte are lithium complex oxidesand lithium oxide materials, such as Li_(1.3)Al_(0.3)Ti_(1.7)(PO₄)₃,Li_(1.07)Al_(0.69)Ti_(1.46)(PO₄)₃, Li₄SiO₄-Li₃BO₃,Li_(2.9)PO_(3.3)N_(0.46), Li_(3.6)Si_(0.6)P_(0.4)O₄,Li_(1.5)Al_(0.5)Ge_(1.6)(PO₄)₃, Li₂O, Li₂CO₃, Li₂MoO₄, Li₃PO₄, Li₃VO₄,Li₄SiO₄, LLT(La_(2/3-x)Li_(3x)TiO₃), and LLZ(Li₇La₃Zr₂O₁₂).

Alternatively, a polymer solid electrolyte such as polyethylene oxide(PEO) formed by a coating method or the like may be used for the solidelectrolyte layer 104. Still alternatively, a composite solidelectrolyte containing any of the above inorganic solid electrolytes anda polymer solid electrolyte may be used.

A separator may be provided in the solid electrolyte layer 104 toprevent short-circuiting between the positive electrode and the negativeelectrode, as necessary. As the separator, an insulator with pores ispreferably used. For example, cellulose; a glass fiber; ceramics; or asynthetic fiber containing nylon (polyamide), vinylon (polyvinyl alcoholbased fiber), polyester acrylic, polyolefin, or polyurethane; can beused.

The negative electrode active material layer 105 may be formed to have asingle-layer or layered structure using one or more of carbon (C),silicon (Si), germanium (Ge), tin (Sn), aluminum (Al), lithium (Li),lithium titanium oxide, lithium niobate, niobium oxide, tantalum oxide,and silicon oxide.

The negative electrode current collector layer 106 may be formed to havea single-layer or a layered structure using one or more of titanium(Ti), copper (Cu), stainless steel, iron (Fe), gold (Au), platinum (Pt),and nickel (Ni). Alternatively, a single-layer or layered conductivefilm including an alloy of the above metals or a compound containing anyof these as a main component may be used.

The positive electrode active material layer 103 and the negativeelectrode active material layer 105 may each include a binder forimproving adhesion of active materials as necessary.

It is preferable for the binder to include, for example, water-solublepolymers. As the water-soluble polymers, a polysaccharide or the likecan be used. As the polysaccharide, a cellulose derivative such ascarboxymethyl cellulose (CMC), methyl cellulose, ethyl cellulose,hydroxypropyl cellulose, diacetyl cellulose, or regenerated cellulose,starch, or the like can be used.

As the binder, a rubber material such as styrene-butadiene rubber (SBR),styrene-isoprene-styrene rubber, acrylonitrile-butadiene rubber,butadiene rubber, or ethylene-propylene-diene copolymer is preferablyused. Any of these rubber materials is more preferably used incombination with the aforementioned water-soluble polymers.

Alternatively, as the binder, a material such as polystyrene,poly(methyl acrylate), poly(methyl methacrylate) (PMMA), sodiumpolyacrylate, polyvinyl alcohol (PVA), polyethylene oxide (PEO),polypropylene oxide, polyimide, polyvinyl chloride,polytetrafluoroethylene, polyethylene, polypropylene, isobutylene,polyethylene terephthalate, nylon, polyvinylidene fluoride (PVDF), orpolyacrylonitrile (PAN) can be preferably used.

Two or more of the above materials may be used in combination for thebinder.

Furthermore, the positive electrode active material layer 103 and thenegative electrode active material layer 105 may each include aconductive additive or the like for improving the conductivity of theactive material layers.

Examples of the conductive additive include natural graphite, artificialgraphite such as mesocarbon microbeads, and carbon fiber. Examples ofcarbon fiber include mesophase pitch-based carbon fiber, isotropicpitch-based carbon fiber, carbon nanofiber, and carbon nanotube. Carbonnanotube can be formed by, for example, a vapor deposition method. Otherexamples of the conductive additive include carbon materials such ascarbon black (acetylene black (AB)) and graphene. Alternatively, metalpowder or metal fibers of copper, nickel, aluminum, silver, gold, or thelike, a conductive ceramic material, or the like can be used.

Flaky graphene has an excellent electrical characteristic of highconductivity and excellent physical properties of high flexibility andhigh mechanical strength. Thus, the use of graphene as the conductiveadditive can increase contact points and the contact area of activematerials.

Note that graphene in this specification includes single-laser grapheneand multilayer graphene including two to hundred layers. Single-layergraphene refers to a one-atom-thick sheet of carbon molecules having πbonds. Graphene oxide refers to a compound formed by oxidation of suchgraphene. When graphene oxide is reduced to form graphene, oxygencontained in the graphene oxide is not entirely released and part of theoxygen remains in the graphene. In the case where graphene containsoxygen, the proportion of the oxygen measured by X-ray photoelectronspectroscopy (XPS) is higher than or equal to 2% and lower than or equalto 20%, preferably higher than or equal to 3% and lower than or equal to15% of the whole graphene.

For the details of the insulating film 107, the description regardingthe insulating film 742 in Embodiment 1 may be referred to.

For the details of the wiring 108, the description regarding the wiring707 in Embodiment 1 may be referred to.

For the battery 100, the positions of the positive electrode and thenegative electrode shown in FIG. 5B may be reversed. That is to say, thenegative electrode current collector layer 106, the negative electrodeactive material layer 105, the solid electrolyte layer 104, the positiveelectrode active material layer 103, and the positive electrode currentcollector layer 102 may be formed in this order from the bottom.

For example, in the case where LiFePO₄ with a thickness of 1 μm is usedfor the positive electrode active material layer 103, the capacity ofthe battery 100 obtained by calculation is approximately 60 μAh/cm².

For example, in the case where LiCoO₂ with a thickness of 1 μm is usedfor the positive electrode active material layer 103, the capacity ofthe battery 100 obtained by calculation is approximately 70 μAh/cm².

For example, in the case where LiMn₂O₄ with a thickness of 1 μm is usedfor the positive electrode active material layer 103, the capacity ofthe battery 100 obtained by calculation is approximately 60 μAh/cm².

Note that each of the above calculations uses the theoretical capacityof the positive electrode active material (i.e., 170 mAh/g for LiFePo₄,137 mAh/g for LiCoO₂, and 148 mAh/g for LiMn₂O₄), supposing that lithiumis used for the negative electrode active material layer 105.

The area and capacity of the battery 100 may be determined in accordancewith the amount of electric power required for a semiconductor device orelectronic device to be connected. In the case where LiFePo₄ is used torthe positive electrode active material layer 103, for example, by makingthe area of the battery 100 (the area where the positive electrodeactive material layer 103 and the negative electrode active materiallayer 105 overlap with each other) greater than or equal to 1 cm² andless than or equal to 100 cm², the capacity of the battery 100 can begreater than or equal to 60 μAh and less than or equal to 6 mAh,according to the above calculation results.

Furthermore, in accordance with the amount of electric power requiredfor a semiconductor device or electronic device connected to thebattery, a plurality of batteries 100 may be connected in series and/orin parallel. In particular, connecting a plurality of stacked batteries100 in series and/or in parallel is preferable because the energydensity of the battery can be increased while the area occupied by thebattery can be reduced.

Structural Example 2 of Battery

FIGS. 6A and 6B show an example of the battery included in oneembodiment of the present invention. FIG. 6A is a top view of a battery120, and FIG. 6B shows a cross-sectional view taken along adashed-dotted line X-Y in FIG. 6A. In FIG. 6A, some components areenlarged, reduced in size, or omitted for easy understanding.

The battery 120 shown in FIG. 6B includes an insulating film 101; apositive electrode current collector layer 102 and a negative electrodecurrent collector layer 106, which are level with each other and arearranged over the insulating film 101; a positive electrode activematerial layer 103 over the positive electrode current collector layer102; a negative electrode active material layer 105 over the negativeelectrode current collector layer 106; and a solid electrolyte layer 104in contact with at least the positive electrode active material layer103 and the negative electrode active material layer 105. The positiveelectrode current collector layer 102 and the positive electrode activematerial layer 103 function as a positive electrode, and the negativeelectrode current collector layer 106 and the negative electrode activematerial layer 105 function as a negative electrode. In addition, aninsulating film 107 is formed over the solid electrolyte layer 104, anda wiring 108 is formed in an opening portion of the insulating film 107.The wiring 108 is electrically connected to the positive electrodecurrent collector layer 102 or the negative electrode current collectorlayer 106.

The battery 120 is different front the battery 100 in FIGS. 5A and 5B inthat the positive electrode current collector layer 102 and the negativeelectrode current collector layer 06 are level with each other and thepositive electrode and the negative electrode exist in the X-Y directionof FIG. 6B. The structure of the battery 120 shown in FIG. 6B makes itpossible to provide a certain distance between the positive electrodeand the negative electrode, whereby short-circuiting between thepositive electrode and the negative electrode can be prevented.

For the details regarding the components of the battery 120, thedescription of the battery 100 in FIGS. 5A and 5B may be referred to.

The positive electrode current collector layer 102 and the negativeelectrode current collector layer 106 in the battery 120 may be formedusing the same materials, at a time. Formation of the positive andnegative electrode current collector layers using the same materials ata time can simplify the manufacturing process.

Structural Example 3 of Battery

FIGS. 7A and 7B show an example of the battery included in oneembodiment of the present invention. FIG. 7A is a top view of a battery130, and FIG. 7B shows a cross-sectional view taken along adashed-dotted line X-Y in FIG. 7A. In FIG. 7A, some components areenlarged, reduced in size, or omitted for easy understanding.

The battery 130 shown in FIG. 7B includes an insulating film 101; apositive electrode current collector layer 102 and a negative electrodecurrent collector layer 106, which are level with each other and arearranged over the insulating film 101; a positive electrode activematerial layer 103 over the positive electrode current collector layer102; a solid electrolyte layer 104 over the positive electrode activematerial layer 103, the insulating film 101, and the negative electrodecurrent collector layer 106; and a negative electrode active materiallayer 105, which overlaps with part of the positive electrode activematerial layer 103 with the solid electrolyte layer 104 positionedtherebetween and is arranged over the solid electrolyte layer 104 andthe negative electrode current collector layer 106. The positiveelectrode current collector layer 102 and the positive electrode activematerial layer 103 function as a positive electrode, and the negativeelectrode current collector layer 106 and the negative electrode activematerial layer 105 function as a negative electrode. In addition, aninsulating film 107 is formed over the negative electrode activematerial layer 105, and a wiring 108 is formed in an opening portion ofthe insulating film 107. The wiring 108 electrically connected to thepositive electrode current collector layer 102 or the negative electrodecurrent collector layer 106.

The battery 130 shown in FIG. 7B is different from the battery 120 shownin FIG. 6B in that the negative electrode active material layer 105 isformed over the solid electrolyte layer 104. The structure of thebattery 130 shown in FIG. 7B makes it possible to provide a certaindistance between the positive electrode current collector layer 102 andthe negative electrode current collector layer 106 for preventingshort-circuiting, and to shorten the distance between the positiveelectrode active material layer 103 and the negative electrode activematerial layer 105 for facilitating the efficient movement of ions.

For the details regarding the components of the battery 130, thedescription of the battery 100 in FIGS. 5A and 5B may be referred to.

For the battery 130, the positions of the positive electrode and thenegative electrode may be interchanged. That is to say, the positions ofthe positive electrode current collector layer 102 and the positiveelectrode active material layer 103 may be interchanged with thepositions of the negative electrode current collector layer 106 and thenegative electrode active material layer 105.

Furthermore, the positive electrode current collector layer 102 and thenegative electrode current collector layer 106 in the battery 130 may beformed through the same step. Formation of the positive and negativeelectrode current collector layers through the same step can simplifythe manufacturing process.

Structural Example 4 of Battery

An example of the battery included in one embodiment of the presentinvention is shown in each of FIGS. 8A and 8B. FIG. 8A is across-sectional view of a battery 140.

The battery 140 shown in FIG. 8A includes an insulating film 101, apositive electrode current collector layer 102 over the insulating turn101, a positive electrode active material layer 103 over the positiveelectrode current collector layer 102, a solid electrolyte layer 104over the positive electrode active material layer 103, an insulatingfilm 110 over the solid electrolyte layer 104, a negative electrodeactive material layer 105 over the solid electrolyte layer 104 and theinsulating film 110, and a negative electrode current collector layer106 over the negative electrode active material layer 105. The positiveelectrode current collector layer 102 and the positive electrode activematerial layer 103 function as a positive electrode, and the negativeelectrode current collector layer 106 and the negative electrode activematerial layer 105 function as a negative electrode. In addition, aninsulating film 107 is formed over the negative electrode currentcollector layer 106. Although not shown in the drawing, the positiveelectrode current collector layer 102 and the negative electrode currentcollector layer 106 are each electrically connected to an externaldevice via a wiring.

The battery 140 shown in FIG. 8A has a region where the insulating film110 exists between the solid electrolyte layer 104 and the negativeelectrode active material layer 105. The insulating film 110 has afunction of preventing short-circuiting between the positive electrodeand the negative electrode.

The insulating film 110 can be formed using, for example, an organicresin of an inorganic insulating material. As the organic resin, forexample, a polyimide resin, a polyamide resin, an acrylic resin, asiloxane resin, an epoxy resin, or a phenol resin can be used. As theinorganic insulating material, silicon oxide, silk on oxynitride, or thelike can be used. In particular, a photosensitive resin is preferablyused for easy formation of the insulating film 110. There is noparticular limitation on the method for forming the insulating film 110.A photolithography method, a sputtering method, an evaporation method, adroplet discharging method (e.g., an inkjet method), a printing method(e.g., a screen printing method or an offset printing method), or thelike can be used.

For the other component of the battery 140, the description of thebattery 100 in FIGS. 5A and 5B may be referred to.

In the battery 140, the insulating film 110 may be formed over thepositive electrode active material layer 103 as shown in FIG. 8B.

For the battery 140 shown in FIGS. 8A and 8B, the positions of thepositive electrode and the negative electrode may be reversed. That isto say, the negative electrode current collector layer 106, the negativeelectrode active material layer 105, the solid electrolyte layer 104,the positive electrode active material layer 103, and the positiveelectrode current collector layer 102 may be formed in this order fromthe bottom.

The structures and methods described in this embodiment can beimplemented by being combined as appropriate with any of the otherstructures and methods described in the other embodiments.

Embodiment 3

In this embodiment, the oxide semiconductor transistor mentioned inEmbodiment 1 will be described with reference to drawings. Note that theoxide semiconductor transistor described in this embodiment is anexample, and the form of a transistor that can be used for the inventionis not limited thereto.

Structural Example of Oxide Semiconductor Transistor

FIGS. 9A to 9D are a top view and cross-sectional views of a transistor600, FIG. 9A is the top view. FIG. 9B corresponds to a cross sectionalong the dashed-dotted line Y1-Y2 in FIG. 9A. FIG. 9C corresponds to across section along the dashed-dotted line X1-X2 in FIG. 9A. FIG. 9Dcorresponds to a cross section along the dashed-dotted line X3-X4 inFIG. 9A. In FIGS. 9A to 9D, some components are scaled up or down oromitted for easy understanding. In some cases, the direction of thedashed-dotted line Y1-Y2 is referred to as a channel length directionand the direction of the dashed-dotted line X1-X2 is referred to as achannel width direction.

Note that the channel length refers to, for example, a distance betweena source (a source region or a source electrode) and a drain (a drainregion or a drain electrode) in a region where a semiconductor (or aportion where a current flows in a semiconductor when a transistor ison) and a gate electrode overlap with each other or a region where achannel is formed in a top view of the transistor. In one transistor,channel lengths in all regions are not necessarily the same. In otherwords, the channel length at one transistor is not limited to one valuein some cases. Therefore, in this specification, the channel length isany one of values, the maximum value, the minimum value, or the averagevalue in a region where a channel is formed.

A channel width refers to, for example, the length of a portion where asource and a drain face each other in a region where a semiconductor (ora portion where a current flows in a semiconductor when a transistor ison) and a gate electrode overlap with each other, or a region where achannel is formed. In one transistor, channel widths in all regions arenot necessarily the same. In other words, the channel width of onetransistor is not limited to one value in some cases. Therefore, in thisspecification, the channel width is any one of values, the maximumvalue, the minimum value, or the average value in a region where achannel is formed.

Note that depending on transistor structures, a channel width in aregion where a channel is formed actually (hereinafter referred to as aneffective channel width) is different from a channel width shown in atop view of a transistor (hereinafter referred to as an apparent channelwidth) in some cases. For example, in a transistor having athree-dimensional structure, an effective channel width is greater thanan apparent channel width shown in a top view of the transistor, and itsinfluence cannot be ignored in some eases. For example, in aminiaturized transistor having a three-dimensional structure, theproportion of a channel region formed in a top surface of asemiconductor is higher than the proportion of a channel region formedin a side surface of a semiconductor in some cases. In that case, aneffective channel width obtained when a channel is actually formed isgreater than an apparent channel width shown in the top view.

In a transistor having a three-dimensional structure, an effectivechannel width is difficult to measure in some cases. For example, toestimate an effective channel width from a design value, it is necessaryto assume that the shape of a semiconductor is known as an assumptioncondition. Therefore, in the case where the shape of a semiconductor isnot known accurately, it is difficult to measure an effective channelwidth accurately.

Therefore, in this specification, in a top view of a transistor, anapparent channel width that is a length of a portion where a source anda drain face each other in a region where a semiconductor and a gateelectrode overlap with each other is referred to as a surrounded channelwidth (SCW) in some cases. Further, in this specification, in the casewhere the term “channel width” is simply used, it may denote asurrounded channel width and an apparent channel width. Alternatively,in this specification, in the case where the term “channel width” issimply used, it may denote an effective channel width in some cases.Note that the values of a channel length, a channel width, an effectivechannel width, an apparent channel width, a surrounded channel width,and the like can be determined by obtaining and analyzing across-sectional TEM image and the like.

Note that in the case where electric field mobility, a current value perchannel width, and the like of a transistor are obtained by calculation,a surrounded channel width may be used for the calculation. In thatcase, a value different from one in the case where an effective channelwidth is used for the calculation is obtained in some cases.

The transistor 600 includes an insulating film 652 over a substrate 640,a stack in which an oxide semiconductor 661 and an oxide semiconductor662 are formed in this order over the insulating film 652; a sourceelectrode 671 and a drain electrode 672 electrically connected to partof the stack; an oxide semiconductor 663 that covers part of the stack,part of the source electrode 671, and part of the drain electrode 672; agate insulating film 653 and a gate electrode 673 that covers part ofthe stack, part of the source electrode 671, part of the drain electrode672, and the oxide semiconductor 663; an insulating film 654 over thesource electrode 671, the drain electrode 672, and the gate electrode673; and an insulating film 655 over the insulating film 654. Note thatthe oxide semiconductor 661, the oxide semiconductor 662, and the oxidesemiconductor 663 are collectively referred to as an oxide semiconductor660.

Note that at least part (or all) of the source electrode 671 (and/or thedrain electrode 672) is provided on at least part (or all) of a surface,a side surface, a top surface, and/or a bottom surface of asemiconductor layer such as the oxide semiconductor 662 (and/or theoxide semiconductor 661).

Alternatively, at least part (or all) of the source electrode 671(and/or the drain electrode 672) is in contact with at least part (orall) of a surface, a side surface, a top surface and/or a bottom surfaceof a semiconductor layer such as the oxide semiconductor 662 (and/or theoxide semiconductor 661). Alternatively, at least part (or all) of thesource electrode 671 (and/or the drain electrode 672) is in contact withat least part (or all) of a semiconductor layer such as the oxidesemiconductor 662 (and/or the oxide semiconductor 661).

Alternatively, at least part (or all) of the source electrode 671(and/or the drain electrode 672) is electrically connected to at leastpart (or all) of a surface, a side surface, a top surface, and/or abottom surface of a semiconductor layer such as the oxide semiconductor662 (and/or the oxide semiconductor 661). Alternatively, at least part(or all) of the source electrode 671 (and/or the drain electrode 672) iselectrically connected to part (or all) of a semiconductor layer such asthe oxide semiconductor 662 (and/or the oxide semiconductor 661).

Alternatively, at least part (or all) of the source electrode 671(and/or the drain electrode 672) is provided near part (or all) of asurface, a side surface, a top surface, and/or a bottom surface of asemiconductor layer such as the oxide semiconductor 662 (and/or theoxide semiconductor 661). Alternatively, at least part (or all) of thesource electrode 671 (and/or the drain electrode 672) is provided nearpart (or all) of a semiconductor layer such as the oxide semiconductor662 (and/or the oxide semiconductor 661).

Alternatively, at least part (or all) of the source electrode 671(and/or the drain electrode 672) is provided next to part (or all) of asurface, a side surface, a top surface, and/or a bottom surface of asemiconductor layer such as the oxide semiconductor 662 (and/or theoxide semiconductor 661). Alternatively, at least part (or all) of thesource electrode 671 (and/or the drain electrode 672) is provided nextto part (or all) of a semiconductor layer such as the oxidesemiconductor 662 (and/or the oxide semiconductor 661).

Alternatively, at least part (or all) of the source electrode 671(and/or the drain electrode 672) is provided obliquely above part (orall) of a surface, a side surface, a top surface, and/or a bottomsurface of a semiconductor layer such as the oxide semiconductor 662(and/or the oxide semiconductor 661). Alternatively, at least part (orall) of the source electrode 671 (and/or the drain electrode 672) isprovided obliquely above part (or all) of a semiconductor layer such asthe oxide semiconductor 662 (and/or the oxide semiconductor 661).

Alternatively, at least part (or all) of the source electrode 671(and/or the drain electrode 672) is provided above part (or all) of asurface, a side surface, a top surface, and/or a bottom surface of asemiconductor layer such as the oxide semiconductor 662 (and/or theoxide semiconductor 661). Alternatively, at least part (or all) of thesource electrode 671 (and/or the drain electrode 672) is provided abovepart (or all) of a semiconductor layer such as the oxide semiconductor662 (and/or the oxide semiconductor 661).

Note that functions of a “source” and a “drain” of a transistor aresometimes replaced with each other when a transistor of oppositepolarity is used or when the direction of current flowing is changed incircuit operation, for example. Therefore, the terms “source” and“drain” can be replaced with each other in this specification.

The transistor of one embodiment of the present invention has a top-gatestructure with a channel length of greater than or equal to 10 nm andless than or equal to 1000 mn, preferably greater than or equal to 20 nmand less than or equal to 500 nm, further preferably greater than orequal to 30 nm and less than or equal to 300 nm.

Constituent elements of the semiconductor device of this embodiment willbe described below in detail.

Substrate

The substrate 640 is not limited to a simple supporting substrate andmay be a substrate where a device such as a transistor is formed. Inthat case, one of the gate electrode 673, the source electrode 671, andthe drain electrode 672 of the transistor 600 may be electricallyconnected to the device.

Base Insulating Film

The insulating film 652 can have a function of supplying oxygen to theoxide semiconductor 660 as well as a function of preventing diffusion ofimpurities from the substrate 640. For this reason, the insulating film652 preferably contains oxygen and more preferably has an oxygen contenthigher than that in the stoichiometric composition, for example, theinsulating film 652 is a film in which the amount of released oxygenconverted into oxygen atoms is 1.0×10¹⁹ atoms/cm³or more in thermaldesorption spectroscopy (TDS) analysis. Note that the temperature of thefilm surface in the TDS analysis is preferably higher than or equal to100° C. and lower than or equal to 700° C., higher than or equal to 100°C. and lower than or equal to 500° C. When the substrate 640 is asubstrate where a device is formed as described above, the insulatingfilm 652 is preferably subjected to planarization treatment such aschemical mechanical polishing (CMP) treatment so as to have a flatsurface.

The insulating film 652 can be formed using an oxide insulating film ofaluminum oxide, aluminum oxynitride, magnesium oxide, silicon oxide,silicon oxynitride, gallium oxide, germanium oxide, yttrium oxide,zirconium oxide, lanthanum oxide, neodymium oxide, hafnium oxide,tantalum oxide, or the like, a nitride insulating film of siliconnitride, silicon nitride oxide, aluminum nitride oxide, or the like, ora film in which any of the above materials are mixed.

Oxide Semiconductor

Typical examples of the oxide semiconductor 600 are an In—Ga oxide, anIn—Zn oxide, and In-M-Zn oxide (M represents Ti, Ga, Y, Zr, La, Ce, Nd,Sn, or Hf). In particular, In-M-Zn oxide (M represents Ti, Ga, Y, Zr,La, Ce, Nd, Sn, or Hf) is preferably used as the oxide semiconductor660.

Note that the oxide semiconductor 660 is not limited to the oxidecontaining indium. The oxide semiconductor 660 may be, for example, aZn—Sn oxide or a Ga—Sn oxide.

In the case where the oxide semiconductor 660 is an In-M-Zn oxide (M isTi, Ga, Y, Zr, La, Ce, Nd, Sn, or Hf) formed by sputtering, it ispreferred that the atomic ratio of metal elements of a target used forforming a film of the In-M-Zn oxide satisfy In≥M and Zn≥M. As the atomicratio of metal elements of such a target, In:M:Zn=1:1 1,In:M:Zn=1:1:1.2, In:M:Zn=3:1:2, and In:M:Zn=2:1:3 are preferable. Notethat the atomic ratios of metal elements in the oxide semiconductor 660vary front those in the sputtering target within an error range of ±40%.

Next, a function and an effect of the oxide semiconductor 660 in winchthe oxide semiconductor 661, the oxide semiconductor 662, and the oxidesemiconductor 663 are stacked will be described using an energy banddiagram in FIG. 10B. FIG. 10A is an enlarged view of the channel regionof the transistor 600 illustrated in FIG. 9B. FIG. 10B shows an energyband diagram of a portion along the chain line A1-A2 in FIG. 10A. Thus,FIG. 10B illustrates the energy band structure of a channel region ofthe transistor 600.

In FIG. 10B, Ec652, Ec661, Ec662, Ec663, and Ec653 indicate the energyat the bottom of the conduction band of the insulating film 652, theoxide semiconductor 661, the oxide semiconductor 662, the oxidesemiconductor 663, and the gate insulating film 653, respectively.

Here, a difference in energy between the vacuum level and the bottom ofthe conduction band (the difference is also referred to as “electronaffinity”) corresponds to a value obtained by subtracting an energy gapfrom a difference in energy between the vacuum level and the top of thevalence band (the difference is also referred to as an ionizationpotential). Note that the energy gap can be measured using aspectroscopic ellipsometer (UT-300 manufactured by HORIBA JOBIN YVONS.A.S.). The energy difference between the vacuum level and the top ofthe valence band can be measured using an ultraviolet photoelectronspectroscopy (UPS) device (VersaProbe manufactured by ULVAC-PHI, Inc.).

Note that an In—Ga—Zn oxide that is formed using a sputtering targethaving an atomic ratio of In:Ga:Zn=1:3:2 has an energy gap ofapproximately 3.5 eV and an electron affinity of approximately 4.5 eV.An In—Ga—Zn oxide that is formed using a sputtering target having anatomic ration of In:Ga:Zn=1:3:4 has an energy gap of approximately 3.4eV and an electron affinity of approximately 4.5 eV. An In—Ga—Zn oxidethat is formed using a sputtering target having an atomic ratio ofIn:Ga:Zn=1:3:6 has an energy gap of approximately 3.3 eV and an electionaffinity of approximately 4.5 eV. An In—Ga—Zn oxide that is formed usinga sputtering target having an atomic ratio of In:Ga:Zn=1:6.2 has anenergy gap of approximately 3.9 eV and an electron affinity ofapproximately 4.3 eV. An In—Ga—Zn oxide that is formed using asputtering target having an atomic ratio of In:Ga:Zn=1:6:8 has an energygap of approximately 3.5 eV and an electron affinity of approximately4.4 eV. An In—Ga—Zn oxide that is formed using a sputtering targethaving an atomic ratio of In:Ga:Zn=1:6:10 has an energy gap ofapproximately 3.5 eV and an electron affinity of approximately 4.5 eV.An In—Ga—Zn oxide that is formed using a sputtering target having anatomic ratio of In:Ga:Zn=1:1:1 has an energy gap of approximately 3.2 eVand an electron affinity of approximately 4.7 eV. An In—Ga—Zn oxide thatis formed using a sputtering target having an atomic ratio ofIn:Ga:Zn=3:1:2 has an energy gap of approximately 2.8 eV and an electronaffinity of approximately 5.0 eV.

Since the insulating film 652 and the gate insulating film 653 areinsulators, Ec652 and Ec653 are closer to the vacuum level than Ec661,Ec662, and Ec663 (i.e., the insulating film 652 and the gate insulatingfilm 653 have a smaller electron affinity than the oxide semiconductor661, the oxide semiconductor 662, and the oxide semiconductor 663).

Ec661 is closer to the vacuum level than Ec662. Specifically, Ec661 ispreferably located closer to the vacuum level than Ec662 by 0.05 eV ormore, 0.07 eV or more, 0.1 eV or more, or 0.15 eV or more and 2 eV orless, 1 eV or less, 0.5 eV or less, or 0.4 eV or less.

Ec663 is closer to the vacuum level than Ec662. Specifically, Ec663 ispreferably located closer to the vacuum level than Ec662 by 0.05 eV ormore, 0.07 eV or more, 0.1 eV or more, or 0.15 eV or more and 2 eV orless, 1 eV or less, 0.5 eV or less, or 0.4 eV or less.

Mixed regions are formed in the vicinity of the interface between theoxide semiconductor 661 and the oxide semiconductor 662 and theinterface between the oxide semiconductor 662 and the oxidesemiconductor 663; thus, the energy at the bottom of the conduction bandchanges continuously. In other words, no state or few states exist atthese interfaces.

Accordingly, electrons transfer mainly through the oxide semiconductor662 in the stacked-layer structure having the above energy band.Therefore, even if an interface state exists at the interface betweenthe oxide semiconductor 661 and the insulating film 652 or the interfacebetween the oxide semiconductor 663 and the gate insulating film 653,the interface state hardly influences the transfer of electrons. Inaddition, since no interface state or few interface states exist at theinterface between the oxide semiconductor 661 and the oxidesemiconductor 662 and the interface between the oxide semiconductor 663and the oxide semiconductor 662, the transfer of electrons is notinterrupted in the region. Consequently, the transistor 600 includingthe above stacked oxide semiconductors can have high field-effectmobility.

Although trap states Et600 due to impurities or defects might be formedin the vicinity of the interface between the oxide semiconductor 661 andthe insulating film 652 and the interface between the oxidesemiconductor 663 and the gate insulating film 653 as illustrated inFIG. 10B, the oxide semiconductor 662 can be separated from the trapstates owing to the existence of the oxide semiconductor 661 and theoxide semiconductor 663.

In the transistor 600 described in this embodiment, in the channel widthdirection, the top surface and side surfaces of the oxide semiconductor662 are in contact with the oxide semiconductor 663, and the bottomsurface of the oxide semiconductor 662 is in contact with the oxidesemiconductor 661 (see FIG. 9C). Surrounding the oxide semiconductor 662by the semiconductor 661 and the oxide semiconductor 663 in this mannercan further reduce the influence of the trap states.

However, when the energy difference between Ec662 an Ec661 or Ec663 issmall, an electron in the oxide semiconductor 662 might reach the trapstate by passing over the energy difference. Since the electron istrapped at the trap state, a negative fixed charge is generated at theinterface with the insulating film, causing the threshold voltage of thetransistor to be shifted in the positive direction.

Therefore, each of the energy gaps between Ec661 and Ec662 and betweenEc662 and Ec663 is preferably 0.1 eV or more, further preferably 0.15 eVor more, in which case a change in the threshold voltage of thetransistor can be reduced and the transistor can have favorableelectrical characteristics.

The band gap of each of the oxide semiconductor 661 and the oxidesemiconductor 663 is preferably wider than that of the oxidesemiconductor 662.

For the oxide semiconductor 661 and the oxide semiconductor 663, amaterial containing Al, Ti, Ga, Ge, Y, Zr, Sn, La, Ce, or Hf with ahigher atomic ratio than that used for the oxide semiconductor 662 canbe used, for example. Specifically, any of the above metal elements inan atomic ratio 1.5 times or more, preferably 2 times or more, furtherpreferably 3 times or more as much as a metal element of the oxidesemiconductor 662 is contained. Any of the above metal elements isstrongly bonded to oxygen and thus has a function of preventinggeneration of oxygen vacancy in the oxide semiconductor. That is, anoxygen vacancy is less likely to be generated in the oxide semiconductor661 and the oxide semiconductor 663 than in the oxide semiconductor 662.

When each of the oxide semiconductor 661, the oxide semiconductor 662,and the oxide semiconductor 663 is an In-M-Zn oxide containing at leastindium, zinc, and M (M is a metal such as Al, Ti, Ga, Ge, Y, Zr, Sn, La,Ce, or Hf) and the atomic ratio of In to M and Zn of the oxidesemiconductor 661 is x₁:y₁:z₁, that of the oxide semiconductor 662 isx₂:y₂:z₂, and that of the oxide semiconductor 663 is x₃:y₃:z₃, each ofy₁/x₁ and y₃₁/x₃ is preferably larger than y₂/x₂. Each of y₁/x₁ andy₃/x₃ is one and a half times or more as large as y₂/x₂, preferablytwice or more as large as y₂/x₂, more preferably three times or more aslargo as y₂/x₂. In this case, the transistor can have stable electricalcharacteristics when y₂ is greater than or equal to x₂ in the oxidesemiconductor 662. However, when y₂ is three times or more as large asx₂, the field-effect mobility of the transistor is reduced; accordingly,y₂ is preferably smaller than three times x₂.

In the case where Zn and O are not taken into consideration, theproportion of In and the proportion of M in the oxide semiconductor 661and the oxide semiconductor 663 are preferably less than 50 atomic % andgreater than or equal to 50 atomic %, respectively, and furtherpreferably less than 25 atomic % and greater than or equal to 75 atomic%, respectively. In the ease where Zn and O are not taken intoconsideration, the proportion of In and the proportion of M in the oxidesemiconductor 662 are preferably greater than or equal to 25 atomic %and less than 75 atomic %, respectively, and further preferably greaterthan or equal to 34 atomic % and less than 66 atomic %, respectively.

The thickness of each of the oxide semiconductor 661 and the oxidesemiconductor 663 is greater than or equal to 3 nm and less than orequal to 100 nm, preferably greater than or equal to 3 nm and less thanor equal to 50 nm. The thickness of the oxide semiconductor 662 isgreater than or equal to 3 nm and less than or equal to 200 nm,preferably greater than or equal to 3 nm and less than or equal to 100nm, further preferably greater than or equal to 3 nm and less than orequal to 50 nm. The oxide semiconductor 662 is preferably thicker thanthe oxide semiconductor 661 and the oxide semiconductor 663.

Note that stable electrical characteristics can be effectively impartedto a transistor in which an oxide semiconductor serves as a channel byreducing the concentration of impurities in the oxide semiconductor tomake the oxide semiconductor intrinsic or substantially intrinsic. Theterm “substantially intrinsic” refers to the state where an oxidesemiconductor has a carrier density lower than 1×10¹⁷/cm³, preferablylower than 1×10¹⁵/cm³, further preferably lower than 1×10¹³/cm³.

In the oxide semiconductor, hydrogen, nitrogen, carbon, silicon, and ametal element other than a main component are impurities. For example,hydrogen and nitrogen form donor levels to increase the carrier density,and silicon forms impurity levels in the oxide semiconductor. Theimpurity level becomes a trap, which might deteriorate the electriccharacteristics of the transistor. Therefore, it is preferable to reducethe concentration of the impurities in the oxide semiconductors 661,662, and 663 and at interfaces between the oxide semiconductors.

In order to make the oxide semiconductor intrinsic or substantiallyintrinsic, for example, the concentration of silicon at a certain depthof the oxide semiconductor or in a certain region of the oxidesemiconductor, which is measured by SIMS, is lower than 1×10¹⁹atoms/cm³, preferably lower than 5×10¹⁷ atoms/cm³, further preferablylower than 1×10¹⁸ atoms/cm³. The concentration of hydrogen at a certaindepth of the oxide semiconductor or in a certain region of the oxidesemiconductor is lower than or equal to 2×10²⁰ atoms/cm³, preferablylower than or equal to 5×10¹⁹ atoms/cm³, further preferably lower thanor equal to 1×10¹⁹ atoms/cm³, still further preferably lower than orequal to 5×10¹⁸ atoms/cm³. The concentration of nitrogen at a certaindepth of the oxide semiconductor or in a certain region of the oxidesemiconductor is lower than 5×10¹⁹ atoms/cm³, preferably lower than orequal to 5×10¹⁸ atoms/cm³, further preferably lower than or equal to1×10¹⁸ atoms/cm³, still further preferably lower than or equal to 5×10¹⁷atoms/cm³.

In addition, in the case where the oxide semiconductor includes acrystal, the crystallinity of the oxide semiconductor might be decreasedif silicon or carbon is included at high concentration. In order not tolower the crystallinity of the oxide semiconductor for example, theconcentration of silicon at a certain depth of the oxide semiconductoror in a certain region of the oxide semiconductor is lower than 1×10¹⁹atoms/cm³, preferably lower than 5×10¹⁸ atoms/cm³, further preferablylower than 1×10¹⁹ atoms/cm³. Furthermore, the concentration of carbon ata certain depth of the oxide semiconductor or in a certain region of theoxide semiconductor is lower than 1×10¹⁹ atoms/cm³, preferably lowerthan 5×10¹⁸ atoms/cm³, further preferably lower than 1×10¹⁸ atoms/cm³,for example.

A transistor in which a highly purified oxide semiconductor is used fora channel region as described above has an extremely low off-statecurrent. In the case where the voltage between a source and a drain isset at approximately 0.1 V, 5 V, or 10 V, for example, the off-statecurrent standardized on the channel width of the transistor can be aslow as several yoctoamperes per micrometer to several zeptoamperes permicrometer.

In the transistor 600 described in this embodiment, the gate electrode673 is formed to electrically surround the oxide semiconductor 660 inthe channel width direction; consequently, a gate electric field isapplied to the semiconductor 660 in the side surface direction inaddition to the perpendicular direction (see FIG. 9C). In other words, agate electric field is applied to the whole oxide semiconductor, so thatcurrent flows through the entire oxide semiconductor 662 serving as achannel, leading to a further increase in on-state current.

Crystal Structure of Oxide Semiconductor

Next, a structure of an oxide semiconductor film is described below.

In this specification, the term “parallel” indicates that the angleformed between two straight lines is greater than or equal to −10° andless than or equal to 10°, and accordingly also includes the case wherethe angle is greater than or equal to −5° and less than or equal to 5°.The term “substantially parallel” indicates that the angle formedbetween two straight lines is greater than or equal to −30° and lessthan or equal to 30°. In addition, the term “perpendicular” indicatesthat the angle formed between two straight lines is greater than orequal to 80° and less than or equal to 100° and accordingly alsoincludes the case where the angle is greater than or equal to 85° andless than or equal to 95°. The term “substantially perpendicular”indicates that the angle formed between two straight lines is greaterthan or equal to 60° and less than or equal to 120°.

In this specification, trigonal and rhombohedral crystal systems areincluded in a hexagonal crystal system.

An oxide semiconductor film is classified into a non-single-crystaloxide semiconductor film and a single crystal oxide semiconductor film.Alternatively, an oxide semiconductor is classified into, for example, acrystalline oxide semiconductor and an amorphous oxide semiconductor.

Examples of a non-single-crystal oxide semiconductor include a c-axisaligned crystalline oxide semiconductor (CAAC-OS), a polycrystallineoxide semiconductor, a microcrystalline oxide semiconductor, and anamorphous oxide semiconductor. In addition, examples of a crystallineoxide semiconductor include a single crystal oxide semiconductor, aCAAC-OS, a polycrystalline oxide semiconductor, and a microcrystallineoxide semiconductor.

First, a CAAC-OS film will be described.

The CAAC-OS film is one of oxide semiconductor films having a pluralityof c-axis aligned crystal parts.

With a transmission electron microscope (TEM), a combined analysis image(also referred to as a high-resolution TEM image) of a bright-fieldimage and a diffraction pattern of the CAAC-OS film is observed.Consequently, a plurality of crystal parts are observed. However, in thehigh-resolution TEM image, a boundary between crystal parts, that is, agrain boundary is not clearly observed. Thus, in the CAAC-OS film, areduction in electron mobility due to the grain boundary is less likelyto occur.

According to the high-resolution cross-sectional TEM image of theCAAC-OS film observed in a direction substantially parallel to a samplesurface, metal atoms are arranged in a layered manner in the crystalparts. Each metal atom layer has a form that reflects unevenness of asurface over which the CAAC-OS film is formed (hereinafter, a surfaceover which the CAAC-OS film is formed is referred to as a formationsurface) or a top surface of the CAAC-OS film, and is arranged parallelto the formation surface or the top surface of the CAAC-OS film.

On the other hand, according to the high-resolution plan-view TEM imageof the CAAC-OS film observed in a direction substantially perpendicularto the sample surface, metal atoms are arranged in a triangular orhexagonal configuration in the crystal parts. However, there is noregularity of arrangement of metal atoms between different crystalparts.

A CAAC-OS film is subjected to structural analysis with an X-raydiffraction (XRD) apparatus. For example, when the CAAC-OS filmincluding an InGaZnO₄ crystal is analyzed by an out-of-plane method, apeak appears frequently when the diffraction angle (2θ) is around 31°.This peak is derived from the (009) plane of the InGaZnO₄ crystal, whichindicates that crystals in the CAAC-OS film have c-axis alignment, andthat the c-axes are aligned in a direction substantially perpendicularto the formation surface or the top surface of the CAAC-OS film.

Note that when the CAAC-OS film with an InGaZnO₄ crystal is analyzed byan out-of-plane method, a peak of 2θ may also be observed at around 36°,in addition to the peak of 2θ at around 31°. The peak of 2θ at around36° indicates that a crystal having no c-axis alignment is included inpart of the CAAC-OS film. It is preferable that in the CAAC-OS film, apeak of 2θ appear at around 31° and a peak of 2θ not appear at around36°.

The CAAC-OS film is an oxide semiconductor film having low impurityconcentration. The impurity is an element other than the main componentsof the oxide semiconductor film, such as hydrogen, carbon, silicon, or atransition metal element. In particular, an element that has higherbonding strength to oxygen than a metal element included in the oxidesemiconductor film, such as silicon, disturbs the atomic arrangement ofthe oxide semiconductor film by depriving the oxide semiconductor filmof oxygen and causes a decrease in crystallinity. Furthermore, a heavymetal such as iron or nickel, argon, carbon dioxide, or the like has alarge atomic radius (or molecular radius), and thus disturbs tie atomicarrangement of the oxide semiconductor film and causes a decrease incrystallinity when it is contained in the oxide semiconductor film. Notethat the impurity contained in the oxide semiconductor film might serveas a carrier trap or a carrier generation source.

The CAAC-OS film is an oxide semiconductor film having a low density ofdefect states. In some cases, oxygen vacancies in the oxidesemiconductor film serve as carrier traps or serve as carrier generationsources when hydrogen is captured therein.

The state in which impurity concentration is low and density of defectstates is low (the number of oxygen vacancies is small) is referred toas a “highly purified intrinsic” or “substantially highly purifiedintrinsic” state. A highly purified intrinsic or substantially highlypurified intrinsic oxide semiconductor film has few carrier generationsources, and thus can have a low carrier density. Thus, a transistorincluding the oxide semiconductor film rarely has negative thresholdvoltage (is rarely normally on). The highly purified intrinsic orsubstantially highly purified intrinsic oxide semiconductor film has fewcarrier traps. Accordingly, the transistor including the oxidesemiconductor film has little variation in electrical characteristicsand high reliability. Electric charge trapped by the carrier traps inthe oxide semiconductor film takes a long time to be released, and mightbehave like fixed electric charge. Thus, the transistor which includesthe oxide semiconductor film having high impurity concentration and ahigh density of detect states has unstable electrical characteristics insome cases.

With the use of the CAAC-OS film in a transistor, variation in theelectrical characteristics of the transistor due to irradiation withvisible light or ultraviolet light is small.

Next, a microcrystalline oxide semiconductor film will be described.

A microcrystalline oxide semiconductor film has a region where a crystalpart is observed in a high resolution TEM image and a region where acrystal part is not clearly observed in a high resolution TEM image. Inmost cases, a crystal part in the microcrystalline oxide semiconductoris greater than or equal to 1 nm and less than or equal to 100 nm, orgreater than or equal to 1 nm and less than or equal to 10 nm. Amicrocrystal with a size greater than or equal to 1 nm and less than orequal to 10 nm, or a size greater than or equal to 1 nm and less than orequal to 3 nm is specifically referred to as nanocrystal (nc). An oxidesemiconductor film including nanocrystal is referred to as an nc-OS(nanocrystalline oxide semiconductor) film. In a high resolution TEMimage of the nc-OS film, for example, a grain boundary cannot be foundclearly in the nc-OS film sometimes.

In the nc-OS film, a microscopic region (for example, a region with asize greater than or equal to 1 nm and less than or equal to 10 nm, inparticular, a region with a size greater than or equal to 1 nm and lessthan or equal to 3 nm) has a periodic atomic order. There is noregularity of crystal orientation between different crystal parts in thenc-OS film. Thus, the orientation of the whole film is not observed.Accordingly, in some cases, the nc-OS film cannot be distinguished froman amorphous oxide semiconductor film depending on an analysis method.For example, when the nc-OS film is subjected to structural analysis byan out-of-plane method with an XRD apparatus using an X-ray having adiameter larger than that of a crystal part, a peak which shows acrystal plane does not appear. Furthermore, a diffraction pattern like ahalo pattern appears in a selected-area election diffraction pattern ofthe nc-OS film which is obtained by using an electron beam having aprobe diameter (e.g., larger than or equal to 50 nm) larger than thediameter of a crystal part. Meanwhile, spots are shown in a nanobeamelectron diffraction pattern of the nc-OS film obtained by using anelectron beam having a probe diameter close to, or smaller than thediameter of a crystal part. Furthermore, in a nanobeam electrondiffraction pattern of the nc-OS film, regions with high luminance in acircular (ring) pattern are shown in some cases. Also in a nanobeamelectron diffraction pattern of the nc-OS film, a plurality of spots isshown in a ring-like region in some cases.

The nc-OS film is an oxide semiconductor film that has high regularityas compared to an amorphous oxide semiconductor film. Therefore, thenc-OS film has a lower density of defect states than an amorphous oxidesemiconductor film. However, there is no regularity of crystalorientation between different crystal parts in the nc-OS film; hence,the nc-OS film has a higher density of defect states than the CAAC-OSfilm.

Next, an amorphous oxide semiconductor film will be described.

The amorphous oxide semiconductor film has disordered atomic arrangementand no crystal part. For example, the amorphous oxide semiconductor filmdoes not have a specific state as in quartz.

In the high-resolution TEM image of the amorphous oxide semiconductorfilm, crystal parts cannot be found.

When the amorphous oxide semiconductor film is subjected to structuralanalysis by an out-of-plane method with an XRD apparatus, a peak whichshows a crystal plane does not appear. A halo pattern is shown in anelectron diffraction pattern of the amorphous oxide semiconductor film.Furthermore, a halo pattern is shown but a spot is not shown in ananobeam electron diffraction pattern of the amorphous oxidesemiconductor film.

Note that an oxide semiconductor film may have a structure havingphysical properties between the nc-OS film and the amorphous oxidesemiconductor film. The oxide semiconductor film having such a structureis specifically referred to as an amorphous-like oxide semiconductor(a-like OS) film.

In a high-resolution TEM image of the a-like OS film, a void may beseen. Furthermore, in the high-resolution TEM image, there are a regionwhere a crystal part is clearly observed and a region where a crystalpart is not observed. In the a-like OS film, crystallization by a slightamount of election beam used for TEM observation occurs and growth ofthe crystal part is found sometimes. In contrast, crystallization by aslight amount of electron beam used for TEM observation is hardlyobserved in the nc-OS film having good quality.

Note that the crystal part size in the a-like OS film and the nc-OS filmcan be measured using high-resolution TEM images. For example, anInGaZnO₄ crystal has a layered structure in which two Ga—Zn—O layers areincluded between In—O layers. A unit cell of the InGaZnO₄ crystal has astructure in which nine layers, including three In—O layers and sixGa—Zn—O layers, are layered in the c-axis direction. Accordingly, thespacing between these adjacent layers is equivalent to the latticespacing on the (009) plane (also referred to as d value). The value iscalculated to be 0.29 nm from crystal structure analysis. Thus, focusingon lattice fringes in the high-resolution TEM image, each of latticefringes in which the lattice spacing therebetween is greater than orequal to 0.28 nm and less than or equal to 0.30 nm corresponds to thea-b plane of the InGaZnO₄ crystal.

The density of an oxide semiconductor film might vary depending on itsstructure. For example, if the composition of an oxide semiconductorfilm is determined, the structure of the oxide semiconductor film can beestimated from a comparison between the density of the oxidesemiconductor film and the density of a single crystal oxidesemiconductor film having the same composition as the oxidesemiconductor film. For example, the density of the a-like OS film ishigher than or equal to 78.6% and lower than 92.3% of the density of thesingle crystal oxide semiconductor having the same composition. Forexample, the density of each of the nc-OS film and the CAAC-OS film ishigher than or equal to 92.3% and lower than 100% of the density of thesingle crystal oxide semiconductor having the same composition. Notethat it is difficult to deposit an oxide semiconductor film whosedensity is lower than 78% of the density of the single crystal oxidesemiconductor film.

Specific examples of the above description will be give., For example,in the case of an oxide semiconductor film with an atomic ratio ofIn:Ga:Zn=1:1:1, the density of single-crystal InGaZnO₄ with arhombohedral crystal structure is 6.357 g/cm³. Thus, for example, in thecase of the oxide semiconductor film with an atomic ratio ofIn:Ga:Zn=1:1:1, the density of an a-like OS film is higher than or equalto 5.0 g/cm³ and lower than 5.9 g/cm³. In addition, for example, in thecase of the oxide semiconductor film with an atomic ratio ofIn:Ga:Zn=1:1:1, the density of an nc-OS film or a CAAC-OS film is higherthan or equal to 5.9 g/cm³ and lower than 6.3 g/cm³.

Note that single crystals with the same composition do not exist in somecases. In such a case, by combining single crystals with differentcompositions at a given proportion, it is possible to calculate densitythat corresponds to the density of a single crystal with a desiredcomposition. The density of the single crystal with a desiredcomposition may be calculated using weighted average with respect to thecombination ratio of the single crystals with different compositions.Note that it is preferable to combine as few kinds of single crystals aspossible for density calculation.

Note that an oxide semiconductor film may be a stacked film includingtwo or more films of an amorphous oxide semiconductor film, an a-like OSfilm, a microcrystalline oxide semiconductor film, and a CAAC-OS film,for example.

For the deposition of the CAAC-OS film by a sputtering method, thefollowing conditions are preferably used.

By reducing the amount of impurities entering the CAAC-OS film duringthe deposition, the crystal state can be prevented from being broken bythe impurities. For example, the concentration of impurities (e.g.,hydrogen, water, carbon dioxide, and nitrogen) that exists in thetreatment chamber may be reduced. Furthermore, the concentration ofimpurities in a deposition gas may be reduced. Specifically, adeposition gas whose dew point is −80° C. or lower, preferably −100° C.or lower is used.

By increasing the substrate heating temperature during the deposition,migration of a sputtered particle is likely to occur after the sputteredparticle reaches a substrate surface. Specifically, the substrateheating temperature during the deposition is higher than or equal to100° C. and lower than or equal to 740° C., preferably higher than orequal to 200° C. and lower than or equal to 500° C. By increasing thesubstrate heating temperature during the deposition, when theflat-plate-like or pellet-like sputtered particle reaches the substrate,migration occurs on the substrate, so that a flat plane of the sputteredparticle is attached to the substrate.

Furthermore, it is preferable that the proportion of oxygen in thedeposition gas be increased and the power be optimized in order toreduce plasma damage at the deposition. The proportion of oxygen in thedeposition gas is higher than or equal to 30 vol %, preferably 100 vol%.

As an example of the target an In—Ga—Zn-based oxide target will bedescribed below.

The In—Ga—Zn-based oxide target, which is polycrystalline, is made bymixing InO_(X) powder, GaO_(Y) powder, and ZnO_(Z) powder in apredetermined molar ratio, applying pressure, and performing heattreatment at a temperature higher than or equal to 1000° C. and lowerthan or equal to 1500° C. Note that X, Y, and Z are each a givenpositive number. Here, the predetermined molar ratio of InO_(X) powderto GaO_(Y) powder and ZnO_(Z) powder is, for example, 2:2:1, 8:4:3,3:1:1, 1:1:1, 4:2:3, 1:4:4, 3:1:2, or 2:1:3. The kinds of powder and themolar ratio for mixing powder may be determined as appropriate dependingon the desired target.

Gate Electrode

The gate electrode 673 can be formed using a metal element selected fromchromium (Cr), copper (Cu), aluminum (Al), gold (Au), silver (Ag), zinc(Zn), molybdenum (Mo), tantalum (Ta), titanium (Ti), tungsten (W),manganese (Mn), nickel (Ni), iron (Fe), cobalt (Co), and ruthenium (Ru);an alloy containing any of these metal element as its component; analloy containing a combination of any of these metal elements; or thelike. The gate electrode 673 may have a single-layer structure or astacked-layer structure of two or more layers. For example, any of thefollowing structures can be employed: a single-layer structure of analuminum film containing silicon; a two-layer structure in which atitanium film is stacked over an aluminum film; a two-layer structure inwhich a titanium film is stacked over a titanium nitride film; atwo-layer structure in which a tungsten film is stacked over a titaniumnitride film; a two-layer structure in which a tungsten film is stackedover a tantalum nitride film or a tungsten nitride film; a three-layerstructure in which a titanium film, an aluminum film, and a titaniumfilm are stacked in this order; a single-layer structure of a Cu—Mnalloy film; a two-layer structure in which a Cu film is stacked over aCu—Mn alloy film; and a three-layer structure in which a Cu—Mn alloyfilm, a Cu film, and a Cu—Mn alloy film are stacked in this order. ACu—Mn alloy film is preferably used because of its low electricalresistance and because it forms manganese oxide at the interface with aninsulating film containing oxygen and manganese oxide can prevent Cudiffusion.

The gate electrode 673 can also be formed using a light-transmittingconductive material such as indium tin oxide, indium oxide containingtungsten oxide, indium zinc oxide containing tungsten oxide, indiumoxide containing titanium oxide, indium tin oxide containing titaniumoxide, indium zinc oxide, or indium tin oxide to which silicon oxide isadded. It is also possible to have a layered structure formed using theabove light-transmitting conductive material and the above metalelement.

Gate Insulating Film

The gate insulating film 653 can be formed using an insulating filmcontaining at least one of aluminum oxide, magnesium oxide, siliconoxide, silicon oxynitride, silicon nitride oxide, silicon nitride,gallium oxide, germanium oxide, yttrium oxide, zirconium oxide,lanthanum oxide, neodymium oxide, hafnium oxide, and tantalum oxide. Thegate insulating film 653 may be a stack including any of the abovematerials. The gate insulating film 653 may contain lanthanum (La),nitrogen, or zirconium (Zr) as an impurity.

An example of a stacked-layer structure of the gate insulating film 653will be described. The gate insulating film 653 contains oxygen,nitrogen, silicon, or hafnium, for example. Specifically, the gateinsulating film 653 preferably includes hafnium oxide and silicon oxideor silicon oxynitride.

Hafnium oxide has a higher dielectric constant than silicon oxide andsilicon oxynitride. Therefore, by using hafnium oxide, a physicalthickness can be made larger than an equivalent oxide thickness; thus,even in the case where the equivalent oxide thickness is less than orequal to 10 nm or less than or equal to 5 nm, leakage current due totunnel current can be small. That is, it is possible to provide atransistor with a low off-state current. Moreover, hafnium oxide with acrystalline structure has higher dielectric constant than hafnium oxidewith an amorphous structure. Therefore, it is preferable to use hafniumoxide with a crystalline structure in order to provide a transistor witha low off-state current. Examples of the crystalline structure include amonoclinic crystal structure and a cubic crystal structure. Note thatone embodiment of the present invention is not limited to the aboveexamples.

Source Electrode and Drain Electrode

The source electrode 671 and the drain electrode 672 can be formed usinga material used for the gate electrode 673. A Cu—Mn alloy film ispreferably used because of its low electrical resistance and because itforms manganese oxide at the interface with the oxide semiconductor 660and manganese oxide can prevent CU diffusion.

Protective Insulating Film

The insulating film 654 has a function of blocking oxygen, hydrogen,water, alkali metal, alkaline earth metal, and the like. The provisionof the insulating film 654 can prevent outward diffusion of oxygen fromthe oxide semiconductor 660 and entry of hydrogen, water, or the likeinto the oxide semiconductor 660 from the outside. The insulating film654 can be a nitride insulating film, for example. The nitrideinsulating film is formed using silicon nitride, silicon nitride oxide,aluminum nitride, aluminum nitride oxide, or the like. Note that insteadof the nitride insulating film having a blocking effect against oxygen,hydrogen, water, alkali metal, alkaline earth metal, and the like, anoxide insulating film having a blocking effect against oxygen, hydrogen,water, and the like, may be provided. As the oxide insulating filmhaving a blocking effect against oxygen, hydrogen, water, and the like,an aluminum oxide film, an aluminum oxynitride film, a gallium oxidefilm, a gallium oxynitride film, an yttrium oxide film, an yttriumoxynitride film, a hafnium oxide film, and a hafnium oxynitride film canbe given.

An aluminum oxide film is preferably used as the insulating film 654because it is highly effective in preventing transmission of both oxygenand impurities such as hydrogen and moisture. Thus, during and after themanufacturing process of the transistor, the aluminum oxide film cansuitably function as a protective film that has effects of preventingentry of impurities such as hydrogen and moisture, which causevariations in the electrical characteristics of the transistor, into theoxide semiconductor 660, preventing release of oxygen, which is the maincomponent of the oxide semiconductor 660, from the oxide semiconductor,and preventing unnecessary release of oxygen from the insulating film652. In addition, oxygen contained in the aluminum oxide film can bediffused into the oxide semiconductor.

Interlayer Insulating Film

The insulating film 655 is preferably formed over the insulating film654. The insulating film 655 can be an insulating film containing one ormore of magnesium oxide, silicon oxide, silicon oxynitride, siliconnitride oxide, silicon nitride, gallium oxide, germanium oxide, yttriumoxide, zirconium oxide, lanthanum oxide, neodymium oxide, hafnium oxide,and tantalum oxide. The insulating film 655 may be a stack of any of theabove materials.

Second Gate Electrode

Although an example in which the transistor 600 has a single gateelectrode is shown in FIGS. 9A to 9D, one embodiment of the presentinvention is not limited thereto. The transistor may include a pluralityof gate electrodes. An example in which the transistor 600 is providedwith a conductive film 674 as a second gate electrode is shown in FIGS.11A to 11D. FIG. 11A is the top view. FIG. 11B corresponds to a crosssection taken along the dashed-dotted line Y1-Y2 in FIG. 11A. FIG. 11Ccorresponds to a cross section taken along the dashed -dotted line X1-X2in FIG. 11A. FIG. 11D corresponds to a cross section taken along thedashed-dotted line X3-X4 in FIG. 11A. In FIGS. 11A to 11D, somecomponents are scaled up or down or omitted for easy understanding.

For the composition of the conductive film 674, the description of thegate electrode 673 may be referred to. The conductive film 674 functionsas a second gate electrode layer. The same potential as that of the gateelectrode 673 or a different potential from that of the gate electrode673 may be applied to the conductive film 674.

The structure and method described in this embodiment can be implementedby being combined as appropriate with any of the other structures andmethods described in the other embodiments .

Embodiment 4

In this embodiment, electronic devices of embodiments of the presentinvention will be described with reference to FIGS. 12A to 12F.

FIGS. 12A to 12F illustrate electronic devices. These electronic devicescan include a housing 5000, a display portion 5001, a speaker 5003, anLED lamp 5004, operation keys 5005 (including a power switch or anoperation switch), a connection terminal 5006, a sensor 5007 (a sensorhaving a function of measuring force, displacement, position, speed,acceleration, angular velocity, rotational frequency, distance, light,liquid, magnetism, temperature, chemical substance, sound, time,hardness, electric field, current, voltage, electric power, radiation,flow rate, humidity, gradient oscillation, odor, or infrared ray), amicrophone 5008, and the like.

FIG. 12A illustrates a mobile computer, which can include a switch 5009,an infrared port 5010, and the like in addition to the above components.FIG. 12B illustrates a portable image reproducing device (e.g., a DVDplayer), which is provided with a memory medium and can include a seconddisplay portion 5002, a memory medium reading portion 5011, and the likein addition to the above components, FIG. 12C illustrates a goggle-typedisplay, which can include the second display portion 5002, a support5012, an earphone 5013, and the like in addition to the abovecomponents. FIG. 12D illustrates a portable game machine, which caninclude the memory medium reading portion 5011 and the like in additionto the above components. FIG. 12E illustrates a digital camera, whichhas a television reception function and can include an antenna 5014, ashutter button 5015, an image receiving portion 5016, and the like inaddition to the above components. FIG. 12F illustrates a portable gamemachine, which can include the second display portion 5002, the memorymedium reading portion 5011, and the like in addition to the abovecomponents.

The electronic devices illustrated in FIGS. 12A to 12F can have avariety of functions, such as a function of displaying a variety ofinformation (e.g., a still image, a moving image, and a text image) on adisplay portion, a touch panel function, a function of displaying acalendar, date, time, and the like, a function of controlling processingwith a variety of software (programs), a wireless communicationfunction, a function of being connected to a variety of computernetworks with a wireless communication function, a function oftransmitting and receiving a variety of data with a wirelesscommunication function, and a function of reading a program or datastored in a recording medium and displaying the program or data on adisplay portion. Furthermore, the electronic device including aplurality of display portions can have a function of displaying imageinformation mainly on one display portion while displaying textinformation on another display portion, a function of displaying athree-dimensional image by displaying images where parallax is utilizedon a plurality or display portions, or the like. Furthermore, theelectronic device including an image receiving portion can have afunction of photographing a still image, a function of photographing amoving image, a function of automatically or manually correcting aphotographed image, a function of storing a photographed image in amemory medium (an external memory medium or a memory medium incorporatedin the camera), a function of displaying a photographed image on thedisplay portion, of the like. Note that functions that can be providedfor the electronic devices illustrated in FIGS. 12A to 12F are notlimited thereto, and the electronic devices can have a variety offunctions.

Each of the electronic devices described in this embodiment incorporatesa plurality of batteries and has a wireless receiving portion capable ofwireless charging.

Usage examples of electronic devices are illustrated in FIGS. 13A and13B.

FIG. 13A shows an example where am information terminal is operated in amoving object such as a car.

The numeral 5103 indicates a steering wheel, which includes an antennainside. The antenna in the steering wheel 5103 can supply electric powerto an electronic device 5100. The electronic device 5100 has a pluralityof batteries, and at least one of the batteries is charged by wirelesscharging. The steering wheel 5103 may be provided with a jig that canfix the electronic device 5100. If the electronic device 5100 is fixedon the steering wheel 5103, the user can make a phone call or avideo-phone call without using his her hands. Furthermore, through voiceauthentication with the use of a microphone provided in the electronicdevice 5100, the car can be driven by a voice of the driver.

For example, by operating the electronic device 5100 while the car isparked, the positional information can be displayed on a display portion5102. Furthermore, information not displayed on a display portion 5101of the car, such as engine speed, steering wheel angle, temperature, andtire pressure may be displayed on the display portion 5102. The displayportion 5102 has a touch input function. Furthermore, one or morecameras to image the outside of the car can be used to display theoutside image on the display portion 5102. That is, the display portion5102 can be used as a back monitor, for example. Furthermore, forpreventing drowsy driving, the electronic device 5100 may operate asfollows, for example: while wirelessly receiving information such as thedriving speed from the car to monitor the driving speed, the electronicdevice 5100 images the driver at the time of driving and when a periodfor which the driver closes his/her eyes is long, it vibrates, beeps, orplays music (depending on the setting that can be selected by the driveras appropriate). Furthermore, by stopping imaging the driver while thecar is parked, power consumption can be reduced. In addition, thebatteries of the electronic device 5100 may be wirelessly charged whilethe car is parked.

The electronic device 5100 is expected to be used in a variety of waysin a moving object such us a car, as described above, and is desired toincorporate a number of sensors and a plurality of antennas that enablevarious functions thereof. Although a moving object such as a car has apower supply, the power supply is limited. In view of the electric powerto drive the moving object, it is preferable that the electric powerused for the electronic device 5100 be as low as possible. For anelectric vehicle, in particular, power consumed by the electronic device5100 may decrease the travel distance. Even if the electronic device5100 has a variety of functions, it is not often that all the functionsare used at a time, and only one or two functions are usually used asnecessary. In the case where the electronic device 5100 including aplurality of batteries, each of which is prepared for a differentfunction, has a variety of functions, only the function to be used isturned on and electric power is supplied thereto from a batterycorresponding to that function; whereby, power consumption can bereduced. Furthermore, batteries corresponding to the functions not inuse, among the plurality of batteries, can be wirelessly charged from anantenna provided in the car.

FIG. 13B illustrates an example in which an information terminal isoperated in an airplane or the like. Since a period in which anindividual can use his/her own information terminal is limited in anairplane or the like, the airplane is desired to be equipped withinformation terminals that the passengers can use when the flight islong.

An electronic device 5200, having a display portion 5202 that displaysimages such as a movie, a game, and a commercial, is an informationterminal with which the current flying location and the remaining flighttime can be obtained in real time, owing to its communication function.The display portion 5202 has a touch input function.

The electronic device 5200 can be fit into a depressed portion in a seat5201, and an antenna installation portion 5203 is provided in a positionthat overlaps with the electronic device 5200, whereby the electronicdevice 5200 can be wirelessly charged while it is fit into the depressedportion. Furthermore, the electronic device 5200 can function as atelephone or communication tool when the user is sick and wants tocontact a flight attendant, for example. If the electronic device 5200has a translation function, the user can communicate with a flightattendant by using the display portion 5202 of the electronic device5200 even when the user and the flight attendant speak differentlanguages. Furthermore, passengers seated next to one another who speakdifferent languages can communicate by using the display portion 5202 ofthe electronic device 5200. In addition, the electronic device 5200 canfunction as a message board, displaying a message in English such as“please do not disturb” on the display portion 5202 while the user isasleep, for example.

The electronic device 5200 has a plurality of batteries each of which isfor a different function, and only the function to be used is turned onwhile the other functions not in use are in an off state, whereby powerconsumption can be reduced. Furthermore, among the plurality ofbatteries, batteries corresponding to the functions not in operation canbe wirelessly charged from the antenna installation portion 5203.

It is difficult to carry a dangerous object on an airplane. Theelectronic device 5200 having a plurality of small-sized batteries ishighly safe, and even if one of the batteries explodes, the damage canbe minimized. In addition, even if one battery becomes unavailablebecause of failure, explosion, or breakage, some of the functions of theelectronic device 5200 can still be used by utilizing the otherbatteries.

The plurality of batteries of the electronic device 5200 provided overthe plurality of seats may be designed such that they can be used inemergency when an airplane has an electrical problem. Since all theelectronic devices 5200, each of which is provided for each of theplurality of seats, are the same products having the same design, asystem may be constructed such that the electronic devices 5200 can beconnected in series as an emergency power supply.

As the plurality of small-sized batteries of the electronic device 5200,one or more kinds selected from the following can be used: a lithium ionsecondary battery such as a lithium polymer battery, a lithium ioncapacitor, an electric double layer capacitor, and a redox capacitor.

The structure described in this embodiment can be used in appropriatecombination with the structure described in any of the otherembodiments.

Embodiment 5

In this embodiment, an example of an artificial organ that is oneembodiment of the present invention will be described.

FIG. 14 is a cross-sectional schematic view of an example of apacemaker.

A pacemaker body 5300 includes at least batteries 5301 a and 5301 b, aregulator, a control circuit, an antenna 5304, a wire 5302 reaching aright atrium, and a wire 5303 reaching a right ventricle.

The pacemaker body 5300 is implanted in the body by surgery, and the twowires pass through a subclavian vein 5305 and a superior vena cava 5306of the human body, with the end of one of them placed in the rightventricle and the end of the other of them placed in the right atrium.

The antenna 5304 can receive electric power, and the plurality ofbatteries 5301 a and 5301 b are charged with the electric power, whichcan reduce the frequency of replacing the pacemaker. Since the pacemakerbody 5300 has a plurality of batteries, the safety is high, and evenwhen one of the batteries fails, the other can function. In this manner,the plurality of batteries function auxiliary power supplies.Furthermore, if the battery to be provided in the pacemaker is furtherdivided into a plurality of thin batteries to be mounted on a printedboard where control circuits including a CPU and the like are provided,the pacemaker body 5300 can be smaller in size and thickness.

In addition to the antenna 5304 that can receive electric power, anantenna that can transmit a physiological signal may be provided for thepacemaker. For example, a system that monitors the cardiac activity,capable of monitoring physiological signals such as pulses, respiratoryrate, heart rate, and body temperature with an external monitoringdevice may be constructed.

If the pacemaker can be small in size and thickness according to thisembodiment, a protrusion generated in the portion where the pacemakerbody 5300 is implanted can be unnoticeably small.

Note that how the pacemaker is placed here is just an example, and itcan be changed in various ways depending on the heart disease.

Furthermore, this embodiment is not limited to the pacemaker. Anartificial ear is an artificial organ that is more widely used than thepacemaker. An artificial ear converts a sound into an electric signaland directly stimulates the auditory nerve with a stimulus device in thecochlea.

An artificial ear includes a first device implanted deep in the ear bysurgery and a second device that picks up sounds with a microphone andsends them to the implanted first device. The first device and thesecond device are not electrically connected to each other, andtransmission and reception between the two are conducted wirelessly. Thefirst device includes at least an antenna that receives an electricsignal converted from a sound and a wire that reaches the cochlea. Thesecond device includes at least a sound processing portion forconverting a sound into an electric signal and a transmitting circuitthat transmits the electric signal to the first device.

In this embodiment, a small-sized battery is provided in each of thefirst device and the second device, whereby the artificial ear can bereduced in size.

Since artificial ears are often implanted by surgery in childhood,reduction in size is desired.

If reduction in size of an artificial ear is achieved by thisembodiment, a protrusion generated in the portion where the artificialear is implanted can be unnoticeably small.

The structure described in this embodiment can be used in appropriatecombination with the structure described in any of the otherembodiments.

Embodiment 6

In this embodiment, an example of a wearable electronic device that isone embodiment of the present invention will be described.

In the case where an electronic device with a complex shape ismanufactured, a plurality of small-sized batteries are placed inpredetermined places as appropriate, whereby the degree of freedom indesign of the electronic device can be increased. As shown in FIG. 15A,an electronic device 5400 has a cylindrical form. In order for theelectronic device 5400 to be worn on the human body, a plurality ofbatteries rather than a single battery are appropriately placed, wherebya feeling of the weight can be reduced. Furthermore, if the device has anumber of functions, consumption of a battery in a standby stateincreases; therefore, batteries for the respective functions areprepared. In the case where the electronic device 5400 having aplurality of batteries has a variety of functions, only the function tobe used is turned on and electric power is supplied from the batterycorresponding to the function, whereby power consumption can be reduced.

The electronic device 5400 is worn on the left upper arm, over a clothes5401, as shown in FIG. 15A. Examples of the clothes 5401 include clotheswith sleeves, such as a military uniform, an assault jacket, a suitjacket, a uniform, and space suits. There is no particular limitation onhow to wear the electronic device 5400, and examples of ways to wear itinclude sewing it on a portion of clothes that overlaps with the upperarm, attaching it with a Velcro fastener (registered trademark) or thelike provided on a portion of clothes that overlaps with the upper arm,fixing it with a band, a clasp, or the like, and binding a band-likeleaf spring around an upper arm.

The electronic device 5400 has an antenna. A perspective view in whichthe electronic device 5400 is worn on the skin and wirelessly charged isshown in FIG. 15B. In FIG. 15B, the electronic device 5400 is worn on anupper arm 5402. A surface of the electronic device 5400 that is to be incontact with the skin is preferably formed using a skin friendly film ora natural material such as leather, paper and fabric. The numeral 5412indicates an electric power transmission device that can wirelesslycharge the electronic device 5400 with the use of a radio wave 5413.When provided with an antenna or a circuit that can transmit and receiveother data, the electronic device 5400 can transmit and receive otherdata as well as power. For example, the electronic device 5400 can alsobe used like a smartphone.

The structure described in this embodiment can be used in appropriatecombination with the structure described in any of the otherembodiments.

EXPLANATION OF REFERENCE

10: device, 11: CPU, 12: battery, 13: regulator, 14: wireless receivingportion, 15: control module, 16; display portion, 17: battery, 18:regulator, 19: display driver circuit, 20: wireless receiving portion,21: display module, 22: communication circuit, 23: battery, 24:regulator, 25: wireless receiving portion, 26: communication module,100: battery, 101: insulating film, 102: positive electrode currentcollector layer, 103: positive electrode active material layer, 104:solid electrolyte layer, 105: negative electrode active material layer,106: negative electrode current collector layer, 107: insulating film,108: wiring, 110: insulating film, 120: battery, 130: battery, 140:battery, 600: transistor, 640: substrate, 652: insulating film, 653:gate insulating film, 654: insulating film, 655: insulating film, 660:oxide semiconductor, 661 oxide semiconductor, 662: oxide semiconductor,663: oxide semiconductor, 671: source electrode, 672: drain electrode,673: gate electrode, 674: conductive film, 700: substrate, 701: plug,702: wiring, 703: plug, 704: plug, 705: wiring, 707: wiring, 720:transistor, 721: impurity region, 722: impurity region, 723: channelregion, 724: gate insulating film, 725: sidewall insulating layer, 726:gate electrode, 727: element isolation layer, 730: transistor, 731:insulating film, 732: insulating film, 740: battery, 741: insulatingfilm, 742: insulating film, 750: transistor, 751: impurity region, 752:impurity region, 753: channel region, 754: gate insulating film, 755:sidewall insulating layer, 756: gate electrode, 757: insulating film,1000: semiconductor device, 1100: semiconductor device, 1200:semiconductor device, 5000: housing, 5001: display portion, 5002:display portion, 5003: speaker, 5004: LED lamp, 5005: operation key,5006: connection terminal, 5007: sensor, 5008: microphone, 5009: switch,5010: infrared port, 5011: memory medium reading portion, 5012: support,5013: earphone, 5014: antenna, 5015: shutter button, 5016: receivingportion, 5100: electronic device, 5101: display portion, 5102: displayportion, 5103: steering wheel, 5200: electronic device, 5201: seat,5202: display portion, 5203: antenna installation portion, 5300:pacemaker body, 5301 a: battery, 5301 b: battery, 5302: wire, 5303:wire, 5304: antenna, 5305: subclavian vein, 5400: electronic device,5401: clothes, 5402: upper arm, 5413: radio wave

This application is based on Japanese Patent Application serial no.2014-026312 filed with Japan Patent Office on Feb. 14, 2014. the entirecontents of which are hereby incorporated by reference.

What is claimed is:
 1. An electronic device comprising: a functionalcircuit; a secondary battery configured to supply electric power to thefunctional circuit; and a regulator connected to the secondary battery,wherein the regulator is configured to prevent an overcharge when thesecondary battery is charged, wherein the regulator comprises aplurality of transistors each comprising an oxide semiconductor in asemiconductor layer, and wherein the oxide semiconductor comprises In,Ga, and Zn.
 2. The electronic device according to claim 1, wherein thefunctional circuit is a CPU, a display driver circuit, or acommunication circuit.
 3. An electronic device comprising: a functionalcircuit; a secondary battery configured to supply electric power to thefunctional circuit; and a regulator connected to the secondary battery,wherein the regulator is configured to prevent an overcharge when thesecondary battery is charged, wherein the regulator comprises aplurality of transistors each comprising an oxide semiconductor in asemiconductor layer, wherein the oxide semiconductor comprises In, Ga,and Zn, and wherein the secondary battery is configured to be wirelesslycharged.
 4. The electronic device according to claim 3, wherein thefunctional circuit is a CPU, a display driver circuit, or acommunication circuit.